Byrd sometimes adds duration to a "measure" as well, which has been notated differently by different editors. I don't see anything particularly amiss.

Just wondering if it as simple as finding the typesetting program wants to add another page with other solutions?

I think its a silly way of typesetting this. This verse is in C (alla semibreve), with the tactus on the Semibreve (whole note), a typical kind of note nere, basically analogous to common time, yet the final note is a Longa (quadruple whole note) which would be incredibly long if actually counted out, so is really only signalling the end of the piece---a common practice, whether in C or cut-C---and needn't really be transcribed literally. What I would have done is kept everything in C (or 4/2 here, with two semibreves to a bar) until the very last bar, which I would have set as two Semi-minims followed by a Breve, or even just a dotted semibreve with a fermata if I didn't feel like reformatting the bar. (Sample attached)

Very helpful, all, thanks!