(Logically, that's the description of a pinch-hitter, but in the past we haven't usually seen pinch-hitters named openly in the guessing-post contributors' lists.)

Not quite true - the contributors' list has always been everyone who made a gift posted before the end, whether they were an original signup or not. It's always included pinch-hitters. We don't identify them as pinch-hitters pe se, and we haven't done that this time.

The list of original signups and finished creators has never matched perfectly.