Yes. The two aren't even the same liturgical genre.

The two are, as Schonbergian says, distinct genres - 1) an office hymn, and 2) a mass Sequence. There is a world of literary difference of usage, form, style, and content, not to mention length between them.

Veni Creator is, as Chonak makes very clear, the office hymn at Vespers of Pentecost. It is also sung at ordinations and at other times.
Veni Sancte has but one use - as the sequence of the Pentecost (Whitsunday) mass.

Substituting one for the other would be illicit, ill-informed, and ill advised.

It's a shame, really, that Catholics have not been taught these sequences and look forward to singing them at Easter, Whitsun, and Corpus Christi the way they look forward to singing 'O Come, All Ye Faithful' and 'Jesus Christ is Ris'n Today' at Christmas and Easter. Many people grumble about singing 'Protestant' hymns at mass, but they really are clueless as to the historic repertory of chant and other historically Catholic music. This is yet another example of how the precepts of the Second Vatican Council went not only unheeded, but were/are purposefully thwarted.

I suspect some of the confusion is due to the Raccolta (1910) having them both as one entry as texts for the Novena.

>> It's a shame, really, that Catholics have not been taught these sequences and look forward to singing them at Easter, Whitsun, and Corpus Christi

Understand your feelings and agree; however while I look forward to Victimae Paschali Laudes and Veni Sancte Spiritus, I admit that I've yet to meet anyone who looked forward to St Thomas' Lauda Sion. His lyrics are beautiful; the melody seems to be hard for anybody's voice range.
Enough to make one go researching polyphonic versions.... hmmm... :)

Chris - if you look forward to singing that, you are a meta person, IMO ;-)
I now return us to the original thread.

I love them all, probably in this order -
1) Victimae paschali
2) Lauda Sion
3) Veni Sancte
4) Dies irae - which we have in the Ordinariate Use but is suppressed in the Roman rite.

Lauda Sion is, of course, one of the longest ever written (including some lengthy ones that Trent suppressed), but is also one of the most musically complex, and is probably the most theologically rich of all. Like many sequences it plays a basically catechetical role in the mass in that it tells a story and lays out the theological significance of it.

I do wish that we had a sequence for Christmas, Epiphany, Ascension, Trinity, Transfiguration, and Christ the King. As I'm sure most here are aware, before Trent every feast and many saints' days had sequences. Some were gems of theological insight, others we are better off without.

We most often use both the sequence and (later in/after Mass) the hymn, on Pentecost.
Is it possible that you tuned in at a time when they were simply using the hymn as a form of incidental music?

@MJO,
If I remember correctly the Lauda Sion melody / meter is used for 5 or 6 of the Adam of St. Victor Sequences, Dom Gueranger also suggests (in translation!) that the Easter sequence Zyma Vetus was also sung to this melody. One problem we have is each sequence is not the same length and so you will find changes in the melody / meter especially towards the end.
The good news is we have metrical translations of all of these sequences. As far as I remember there is not an Adam of St. Victor sequence for Ascension, In the ancient french books they sometimes used older? or at least other sequences.
What I will do in my spare time over the next couple of days is create a list with links to the music of all of the Lauda Sion melody sequences, I will also link to the metrical translations by DIGBY S. WRANGHAM.

For the Ascension Rex omnipotens die hodierna is listed, this is a sequence found in the Sarum Sequentiarium so the Sarum chant website should have an English version. I could not quickly find it so looked in the other books on the Sarum Sequences, English translation and English chant

Ah got it! Ascension, and much more. Volume 2 and Volume 3, grand total of 103, plus hymns, and some more of doubtful attribution.
Maybe too much similarity of approach for frequent liturgical use.

I see @a_f_hawkins has found some of these links before I have had time to post. We have a number of threads on this forum with these links now!
The Sequences of St Adam of St. Victor can be found in this book,
it has critical discussions of the text and music in French, and in the last part the music is written out in full for each Sequence.
The Translations by DIGBY S. WRANGHAM can be found in these books, Vol 1, Vol 2, Vol 3,
Here are listed 72 Sequences from I think a French Liturgical book, the ones in Italics do not appear to be written by Adam so are not discussed. The following use a melody similar to the Lauda Sion.
Heri mundus exultavit St Stephen Latin chant, and English translation
Laudes Crucis attollamus Holy Cross Latin chant, and English translation.
Postquam hostem et inferna Sunday within the Octave of Ascension Latin chant, and English translation.
Lux iocunda, lux insignis Feria II Pentecost Latin chant, and English translation.
Profitentes unitatem Trinity Latin chant, and English translation.
Corde, voce pulsa celos St Paul Latin chant, and English translation.
Latabundi iubilemus Transfiguration Latin chant, and English translation.
Laus erumpat ex affectu St Michael Latin chant, and English translation.

Also according to Gueranger, Zima Vetus expugetur Latin chant, and English translation.
The other Sequences on this page may also fit the Lauda Sion melody / meter.

While Digby S Wrangham has produced metrical translations I wonder if they really would be something you would want to sing. Anyway since the GABC code for the Laudes Crucis attollamus has been uploaded to Gregobase (see link above) it would not be too difficult to swop the words over to produce the other Sequences above. The music will need editing for some of the above. I am in the process of producing modern chant editions of a number of the Sequences above, but they need quite a bit of proof-reading.

A caution about the books by Wrangham: He just labels the Postquam hostem as Ascension whereas it is intended for the Sunday within the Octave, not Ascension Day. Other references may be equally imprecise, it was regrettably common among Anglican 'antiquaries' (if there is an established less derogatory term I will be happy to edit it in).

@CCooze, I’m sure. These parishes also had their worship aids posted online, and Veni Creator was indeed the listed “sequence.”

The Analecta Hymnica notes Postquam Hostem as

liturgische verwendung ist durchweg für "Dominica infra Octavas Ascencionis"
liturgical use is consistently for "Dominica infra Octavas Ascencionis"

I have only checked one source, the Missale Parisiense 1481, which gives Rex omnipotens for Ascension Day and Postquam Hostem for Dominica infra octavas ascencionis
YMMV

They don't disagree. Cantus quotes the rubric for Postquam hostem, but each of the sources listed also contains Rex omnipotens and in each case that rubric is in die ascensione. So the Analecta Hymnica has drawn a conclusion.

tomjaw :The first listed in Cantus seems not to be in the Analecta's list F-DOU 123. It is described as "Calendar, with sequences listed, each given a number". There are some pages of that source online - it is from Marchiennes and local to Douai - but not relevant ones.
Postquam hostem et inferna spoliavit : In ascentione domini l : F-DOU 123 36v 050 ;
Rex omnipotens die hodierna : In die ascensionis c.liii : F-DOU 123 98v 151 ;
So the document numbers the sequences, as 50 & 153, and has them 62 pages sheets apart, hmmm.
A paper by Christian Meyer contains only notated pieces from Marchiennes, so neither there nor in his database .
One might speculate that Marchiennes had been established for half a millennium before Adam wrote Postquam, and it was 'not invented here', also do I need to write out the Lauda Sion tune again!.

Returning to the Pentecost sequence, Michael P. Foley has pointed out at NLM that the text of verse 6 has been changed. Analecta Hymnica shows the original lumine, rather than homine in the second line. The notes on p.237 seem to prefer lumine, but my German is nonexistent. I do like Caswall's rendering of the official Latin text

If Thou take Thy grace away,
Nothing pure in man will stay;
All his good is turned to ill.

And I was displeased when the Mass I was watched online omitted the sequence.

The notes on p.237 seem to prefer lumine, but my German is nonexistent

You are right. May I give it a try?

... these are indeed a lot of sources favoring the traditional text, opposed though by the same amount including old sources of weight.
"Nihil est in homine" especially in connection with the following "Nihil est innoxium" is almost a banal statement; against which the more subtle reading ('lectio difficilior') of "Nihil est in lumine" must be considered to have a profound and well-focused meaning:
"Without thy Devine Splendor, nothing is in the right light, and nothing will flourish."