[AJFmzk]

Typically an artist will write a ton of songs for an album, demo a certain percentage of those and then fully record and produce a portion of the demos. For example if you write 40 songs, demo 15-20, 10-15 will be fully worked/released (the numbers are arbitrary, but you get the idea). Artists that have others compose for them will sometimes skip the first step and go straight to working on demos. Ayu has produced so many songs and released so many with multiple albums a year, it's entirely possible that she turned all of the demos into full songs and released most of them. It's also possible that there are ton of unreleased demos just from sheer quantity, that she decided not to release but it's hard to determine which situation it is. Probably somewhere in between, since she recycled material for Love Again, but I really wouldn't be all that surprised if she has very few unreleased songs that went to production. It costs a label a lot of money to fully produce a polished pop-rock song, like thousands of dollars for a single song, so if they never gets released it's a significant loss.