PSA: if you use Netpass and you want to check if you've gotten anything new, go to the home menu (suspend, not close) and go to the "Notifications" menu at the top. Quite convenient as they are timestamped and tell you how many out of the total streetpasses for that game you got!
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by "total streetpasses" i mean the amount of streetpasses a game can get before it doesn't accept/use any more. For example, in Streetpass Mii Plaza, the max is 10.
Just wanted to pass that along in case anyone else were to find it as useful as I did! :D