Source for this assertion? AFAIK Byrd's original was indeed in F.The edition in F doesn't appear to be Byrd's original, but a transposition.
As eminent musicians have said to me with a wink, "the dark ages".c. 1961
When using this Mass liturgically, what is (or, was) done with the Kyrie? It seems not to repeat the invocation three times, as in the mass-book. Just asking'.
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