To agree with, and paraphrase, Upsetter, 'Now that's what I call a proper Listener puzzle'. I found it harder than some other contributors appear to have done - largely because, with only three cross-checked letters to begin with (at 4, 6 and 18) I had to cold-solve about two-thirds of the clues to get started. Even then, I only began to make headway after cracking 15, 29 and 38 (getting held up with the last of those because BRB doesn't suitably define one of the wordplay elements).
Like others, I'm pleased we've been given - dare I say it - carte blanche in dealing with the blank cells, which we weren't in the recent comparable puzzle; and I too wondered about the 'eighth' thematic entry, which certainly looked as if it was intended to be one. Can Chalicea comment without giving anything away?
I also thought there should have been an entry/clue for an earlier 13 with subsequent clues re-numbered. The final grid isn't as tidy thereabouts as it is pretty much everywhere else.
But thank you, Chalicea. The unclued entry was a pleasing touch as well!