I agree that any ambiguity as to what to highlight is resolved by the corrected letters- and that does leave 49 cells. (THough we could also have had TORCH and both types of gun in full. I can't remember who found/spotted only two crosses, but in case you haven't spotted the third yet, they are TAU, CROSS and ROOD. (Though one might mischievously suggest "ireful" and "stern" too!)
But I am still left with a question:
What on earth is 21d? I mean, it has to be SUMY, doesn't it? But what IS that? I'm presuming an E for the I of "tinder", so looking perhaps for a currency - bit finding nothing.