If you don't call it, does it count? Can you brag about it later?
Yes. Talent doesn't need to brag (which probably explains why I'd have to scream it through a megaphone!)
If you call it late, does it count?
If you don't mean it, can you call it?
Yes, because its outrageous luck, which should also be celebrated
If you don't collect it, and concede possession, does it count?
No, but if you win the ball back at least you dont look like a twat!
If you use it to pass to a teammate successfully, is that OK?
Yes, but you should reserve the right to hold the moral high ground if said team mate then fucks up the move by dribbling the ball out for a goal kick from 25 yards.
If it clips a leg on the way through, does it count?
Yes. Any part of the body apart from the hand/arm (unless you're the keeper of course, in which case you can roll the ball through the opposition players legs).