Not sure if I'm going to finish this!!
There may be superfluous letters - 3 across: Gather plot developer is short of central characters (9) ?ARG?R??E 42 across: Verse form only encountered in Greek lines (9 two words) L????????
Also 'six entries are affected by shortages; answers to the corresponding clues must be entered as jumbles' So? corresponding clues are anagrams, but what do they mean by corresponding?
Gosh I'm feeling thick!
Thanks in advance.
The six entries have answers that are too short, but when you add letters (gleaned from the superfluous letters) the 'shortage' is evident. I guessed 19 A and 32 A. (I tidied up the letters later).
The answer to the clue for 3a is GARNER (def 'gather') wordplay = 'GAR(dn)ER' = 'plot developer' (minus centre).
So, the letters for GARNER are jumbled in the 6 cross-checked squares of 1ac (and then the unchecked squares are filled in to make an item that could suffer from shortages).
42 wordplay = 'only' = LONE (around) MET inside GR(eek).
19ac is a 'shortage' but not 32a, which is normal (maybe Nical meant 33a, which is a 'shortage').