Hello Michael, I had a look at library.db again. Do I get this right:

Every browsable menu level (album, year, genre) has its own table (with the exception of the multipurposed contributor. Why?)

And another question:

The Custom Scan tables are in persist.db in one huge table. Loading the Custom Browse menus sometimes(?) is very slow, I might even get timeouts (what would speed it up: a faster disk, more RAM, a faster CPU?). Is this because the table is not split into "entry points" like the native tags but is just one large list?