I have several thousand pieces of sheet music, and who knows how many pages. I have it three-hole punched and organized in individual hard-backed binders by composer, then for composers that I have less music for e. g. Couperin, I have it organized by Period / Style. This is all cataloged in a searchable spreadsheet, organized in order as they appear on my bookcase, and I have a printed out copy of it.
It actually never occurred to me that this isn't entirely common but almost ALL of my sheet music is loose because it's copies from books, or printed from the computer, or just randomly found from somewhere. I own quite a few books as well but I don't typically purchase books for heavy use, more just to bolster my music library. Anyway, I use binders. I have something like 18 of them right now, although that's partially because I use smaller ones because they're less likely to break. Everything that goes into them is in page protectors so I have lots of those as well.
They're not randomly tossed into the binders. For some composers, I have so much stuff by them that I use one binder for everything from that composer.
I also have four binders for everything I've composed. I keep everything from the choirs I sing with separate from everything else, so those are in their own binders.
The rest of the binders are alphabetized by composer. In addition to my binders and all my books, I do also have a file cabinet of music which I keep organized by composer as well. It's filled with everything that I don't really touch. Either it's old stuff that I've kinda let go of, or stuff that I printed out/got but never got around to because I didn't care enough. So that's kinda my "storage". I ALSO have all of my pdfs on my computer very nicely organized by composer in folders. It's all in one place, labeled the same way, easy to search and print. So that's an extensive collection as well. As far as LABELING all of these things, my binders have labels on the cover so I know what the binder contains and like I said, they're alphabetized on the inside. My file cabinet has every composer labeled with, well. a label.
Easy to see. And my computer has everything labeled by composer as well.