Chris, I don't think it's that at all. The first word of 10a is the answer. Every single character after that, including the '-', is needed to get that answer. 'lOver' uses lift-and-separate to give 'l' for left, which is a reversal indicator in an across clue. So everything to the left of the final word is reversed, including the '-', and gives the first four letters of the answer. The rest of the final word just gives the final letter. Of course, this might be completely wrong, but I don't think it is.