I hate that the Liber doesn't have an index. I mean, I am sure it would be quite large, so I'm not really surprised.
The Gregorian Missal does, but it's subdivided into all the categories for the propers, so you still have to read through each category, but that's usually what I use when I need to find a chant.
However...while I'm on the topic of making an index...what about an index for everything for all Gregorian Chant?
Here's what my perfect index would contain for all the chants:
-by scripture reference
-by Latin first words
-while I'm at it, how about an index containing all of the major Latin words in it (like, this happened to me--I knew the chant I couldn't remember contained the Latin words "king" and "beauty" in it. wouldn't that have been great if I could have just pulled out my index and looked up all the chants containing the word "rex" in them!?)
-and I might as well have an index containing all the English translations of the important words in the chants!
(this all stemmed from the fact that I have an old book from ocp something about "organ meditations on gregorian themes," and the titles of all the pieces are in English! So this one I really liked, was called "you are the honor of your people" or maybe it was "our people," I can't remember. So I was like how on earth am I going to find it? I don't even know how to translate that into Latin! much less what word would be first even if I had a Latin index... well, before I wrote this whole post, it really only took me 5 minutes of doing a few google searches to find that the chant I'm looking from is [I think, but I'll have to check when I have the book with me,] from the Immaculate Conception Gradual, from the middle of it, and the Latin is "tu honorificentia populi nostri.")
eh, who needs an index when you've got the internet?