>>No bar numbers, so if you get lost you are left high and dry if you are one to a part.
I took part in a workshop decades ago where we had the opportunity to try, very briefly and casually, singing from a Renaissance score, and found that to be exactly the problem -- there's no reference point. Unfortunately, that experiment was during a lecture (by David Skinner IIRC), with 60 or 80 people of a wide mix of skills and experience, seated in rows in a lecture-style class, and predictably, it crashed and burned once or twice and there wasn't time to keep trying. (Dang. I really wanted just one more shot at it.)
I think it would work out if the singers basically learned their parts and how they fit together by repetition in rehearsal, and then only needed the score during services as a kind of aide de memoire, a shorthand crib. Which is more or less how most of us sing pieces we know well today, after all. But I don't picture Renaissance choristers just standing up and sight-singing largely error-free, the way good readers can from a modern vocal score.
Unless perhaps their memory and counting skills were simply much more developed by practice? I think actually we've had this conversation before, but anyway -- I picture it as analogous to the way the human brain gradually transitioned, first from oral to written culture, and then from reading aloud, sounding out words more slowly, to modern speed reading, skimming over entire phrases and even paragraphs at a glance. I can't remember whether people in the 16th century still went into another room to read a private letter, for example, because 'reading' was not generally silent. I don't recall exactly when that changeover happened; perhaps mostly earlier, before the printed book, but it might still have been evolving to some extent.
Anyway, I would totally be up for it in principle, and to visit your early-music group as well, if we ever reach the post-pandemic era. (-: Though it's been a long time since I played recorders, and longer ago any other instrument. Somehow picturesque English villages like the fictional Midsomer seem better supplied not only with gruesome murders, but also with people interested in those kinds of creative pursuits. Here in Texas outside major cities it doesn't seem to go much beyond cosplay, like SCA.