I've finished the puzzle – including the endgame which gave me much less of a headache than many here have reported. (I did complete the previous Listener puzzle that employed this idea, so obviously that was a massive help.)
However, for the sake of completeness, I need help with parsing.
Initially, I had 'Malaysian' in 8dn as an extra word, since the clue works just as well with the entry in the BRB without it. However, 'Malaysian' does not fit with the thematic link I have for the down clues. So I have six correct extra words taken from down clues. Their last letters can be arranged to make PERTLY. Can I have a hint to the last extra word in the down clues or it's clue, please?
Also I have the required seven extra words from the down clues, but I can't parse 37ac without removing the first word, even though it seems like it should be a 'normal' clue.