How to restore old iTunes libraries/missing Apple Music songs?

Hi all,

Apple Music on PC deleted all of my songs, so I re-authorized the computer and dragged some of my files back in, but there's a heap of songs missing. I can see whole albums that haven't come across, for example.

I re-downloaded from purchased and they're still missing, so I assume this is a hangover from iTunes where you used to buy songs directly rather than download them through Apple Music. Is there a way to access these Apple Music files?

I also have backed up my old libraries, but Apple Music says it doesn't recognise .itl files. Some of my old libraries have also been renamed iTunes Library (Damaged).

I'm on a PC, if that helps - I see some advice about converting .itl on Mac programs but can't see the PC one.

Thanks!