A lot of bands and that generally hit their creative peak within a couple of albums, and it’s ever-diminishing returns afterwards. However, some hit that commercial sweet-spot later on where they attract the attentions of everybody, or simply just attract your own attentions despite them having a wealth of earlier material which has been completely out of your purview.
This probably doesn’t happen quite so much in the information age - but I’ll go first with stuff I’ve jumped onto during mid-career or late career. Thread has probably been done before.
For me, it’s:
Depeche Mode - Ultra (Remember watching them on TOTP doing “Barrel of a Gun” and thinking they were cool as fuck.)
Mercury Rev - All is Dream (Used to get a friend to tape MTV2 for me as we didn’t have Sky, and “Nite and Fog” was just this lush, blissful track.)
Ryan Adams - S/T (Had never listened to him but loved this album during a bit of a difficult time.)
Manics - Everything Must Go (Similar to my experience with Depeche Mode, in the charts when I was a nipper.)
David Bowie - Hours (He was in some video game round about the time it was released and in gaming mags, and was embracing MP3 and that. Fucking blew my mind by the time I got round to Ziggy Stardust.)