I think the Os are safe enough, roslyn, but there are fewer Cs and they're never doubly checked by both across and down clues (so you'd have to be missing one altogether to fall short of the count).
I'd entered something very early on and forgotten all about (it fits the definition pretty well and has a letter missing in the wordplay - but not one that works thematically by itself).
My 6th C is on the row directly above my final O (symmetrically opposite, L to R).