I completed the difficult crossword challenge today, and then picked up the crossword epic. The crossword epic says "no crosswords completed yet" despite me having completed the one for the difficult challenge (which fits the criteria for being counted). Is the epic crossword not supposed to count ones done before the challenge?

I think it only counts what you do after the challenge is issued anything done before that does not count.

Correct. You haven't completed any since you got the new challenge.