This was trash

Head-scratcher until the lightbulb went off. Unusual, but quite a delight. Covers a lot of ground but pulls together nicely.

Thank you!! This was so much fun!! I didn’t get all the categories correctly, but I loved the reveal!! 🥰

The initials were a little bit too hard and arcane for me, but I did enjoy the heather/cracker connection.
btw
the song was actually not by MM, but by The Exciters.

You're right...that the song was first recorded by The Exciters. That was in 1963. In 1964, Manfred Mann released it version, and I believe that was the one that gained the dominant airtime. In most references, they're listed as the vocal group.

The 'obscure references' were to several commenters who post in the 'Connections' subsection of the comments to the NY Times Wordle review column, Some folks are dedicated in solving regular PuzzGrids that I put up here. The categories 'MM,' 'KP,' and 'Documents,' as well as the 'Heather' clue were designed as tributes to them. I know that makes it a rather parochial PuzzGrid, but I think they all got a kick out of it. Are you a commenter there as well?