Picking a version of O Sanctissima is a bit like choosing chocolate. This one takes the harmony from Ludwig von Beethoven and the words from the Mass Book. The old red books stop at the first two verses - which is probably a wise thing - but my edition has five verses, just in case.
Here’s a very pleasant recording with the repeats as Beethoven wrote it. I took out the repeats in the above, but consider the repeats good for learning. As far as I can tell the harmony is the same.
The words are probably different. It’s one of those hymns which has lots of various verses. I can’t remember where I pulled these words from, but that’s where we’re stuck until the next edition of the Mass Books.