Wait, you read a number on the bottom of a mug and decided that settles it? Those stamps are all over the place. A "12 oz" mug usually means 12 oz filled to the very top lip, and nobody pours coffee to the brim unless they hate their keyboard. Fill it to a normal drinking level and you're back around 9 or 10 oz, so your old guess was probably closer than you think. Also a coffee "cup" on a pot is 5 oz, not 8, so the whole thing is made up anyway.

Mine was root bound too, so I sized up the pot and it bounced back fast.

Been there way too many times and it never stops stinging. Had a tile job once where one crooked stud threw off the whole wall and I didn't catch it until the third row, so I tore out half a day of work over something smaller than my pinky. You just gotta laugh so you don't cry and double check that first course next time.