BlueCat that is very interesting that you were able to track those last playthrough bets. I will try one of the codes floating about and watch the math as well and let ya know what comes of it.
Sometimes these casinos only credit a particular bet with a percentage of the bet toward the playthrough req. e.g. $5 bet on a slot game may reduce the playthrough by 100% or $5 (100% X $5 = $5) but another game such as blackjack may be worth 75% per bet or $3.75 (75% X $5 = $3.75).
Could this have been what happened in your case? Of course, the games and percents in the example were grabed out of the air by me, but hope I made my point.
If you were playing slots, most slots are at 100% and this most likely does not explain it. I just wish these casinos would trim down the terms to something simpler. e.g. instead of 20X make it 21X and not worry about all the different game b s! Using the "laws of large numbers", figure out the needed playthrough multipler to make their financial statement about the same! At ISU the class was called STAT101! Although, I admit, the class was a *****! lol