If I am correct that the clue formed by the extra letters comprises 10 words, is the purpose of the 8th & 9th ones (2,1) at 21d, 23d and 25d simply to link the wordplay to the definition ?
That's how I see it, Son1. I feel that the two-letter preposition should really be used in "definition from wordplay" constructions rather than the other way round (as here), but I'm probably being anal-retentive.
I appear to have satisfactorily resolved everything except 34Across, for which I have LO?TE. I have absolutely no idea how this clue works, and would appreciate a not too subtle, heavy-handed nudge, please. I've assumed the extra letter to be G.
I think it might be a double definition &lit with 'alternately' doing double duty as part of the def 'or' + anagrind for - LET (g)O [the (g) is extra] +S and 'originally' doing double duty for the S - '(S)penser' + 2nd def for LOSTE (the 1st being 'let go' [past tense].
This time have had a good run except for SE corner. Can anyone help me with 28 down - I did not study Latin and often struggle. Also 32 down - I can't parse the clue and here identify the surplus letter.
If I could resolve these two I'll struggle on to the next stage, so any help appreciated.