I’m not stuck on that as a defining feature - I was trying to be clear but probably went too specific. The point I was trying to make is it’s substantially bigger than an album or even a double album.
My intention was not to just cover multiple albums more than two from the same artist, but also very large compilations both for the same artist and various artists. e.g. The Jazz Masters with hundreds of recordings spanning a career and Trojan box sets with ~50 recordings from various artists (and they don’t come in boxes though the packaging is cardboard). Bowie’s Five Years: 1969-1973 compiles albums and new compilations of B-sides together.