I play Tap ranch which at times gives free points for downloading free apps. I've downloaded all free apps and have deleted them but when I try to download it again I dont get the free points. Is there a way to delete the memory of already downloaded games so I can receive the free points again. Thanks for helping.
My understanding is the device UDID is being sent in to the servers for each game.
Just click on the serial number in iTunes to reveal your UDID.
They see that your device showed up as a first launch of that game, so they don't actually know that you bought the app today and downloaded it. For privacy reasons, Apple has severely restricted how apps talk between themselves on your phone, so it's far more likely they are doing the matching and tracking on their game servers. (plus+, open feint, etc...)
I believe you would have got the bonus if you coincidentally ran game B after game A - even if you didn't actually see the offer. You could test this by downloading the app on another device using your account and see if they can tell you or just your device.
Why don't you ask the company that made the games how they knew? They might just tell you.