During the past, I made the mistake of buying several music selections that have statements such as: "Trumpet/Saxophone" or "For all Bb Instruments" or "Clarinet/Saxophone/Trumpet/Cornet." While the writer intended that the music fit multiple instruments, I have found the results to be unsatisfactory. Combination music tends to fit none of the instruments well and the range is often a problem. Any music written for Bb Trumpet CAN be played on the Bb Cornet, the Bb Baritone, and the Bb Fluglehorn, (even Bb mellophones and bass trumpets) and vice versa, whether that is stated or not. The converse is also true. At this point it is necessary to look at the range and level of difficulty. If the seller states "I am not a musician but I will try to answer all questions...." that is a signal to ask the seller to email you pictures of a couple of selections. Doing this costs the seller nothing extra through eBay and it allows the prospective buyer to look at some of the sample music to determine range and level of difficulty. The prospective buyer can also request READABLE pics of the table of contents to avoid buying song titles already in hand. Many sellers automatically provide sample music and table of content pics on their original eBay ad, which is great.
If you are a music COLLECTOR, please do not read this paragraph! I buy music to play, not to collect and put in clear plastic covers for posterity. It has been my observation that loose sheets in books of music, broken spines, even torn pages, are not a problem if you intend to play it. I simply make tape repairs and cut off the spine of the book/sheet (and sometimes even sacrifice the top margin and bottom margin, resulting in often cutting off some of the publication data--I TOLD you COLLECTORS not to read this!) with a ruler and an exacto knife. Then I use a three hole puncher and put the music in three hole, three inch binders. It is simple to type up a table of contents page for each binder.
Additionally, I have found that music written for organs is excellent for Bb instrument players as long as the above guidelines on difficulty level and range are followed. The organ treble cleff line can be played solo by any Bb instrument and with an organ or piano if you have a C instrument. I have found most all piano music written in a range entirely to high for my ability, but there is some out there that is reasonable. This is another way of getting good music to play on Bb instruments, since such music written for a SPECIFIC instrument is more limited.