No need to apologize ... as far as I know there are 2 ways to find out which ID was used to buy what apps.
Log into one of your accounts on iTunes on your computer and look at your purchased history. Store>View my account - from the iTunes menu. You can view all of your purchases in there for each account. Scrool down to Purchase Hostory and tap on the blue arrow "See All" on the right side.
You can also go to the app store on the iPad - and tap on the purchased tab - and see all of your purchases in there. You can go to iTunes on the iPad and do the same thing.
You just have to remember to log into that account in order to see what you have purchased with it.