I use my Vita more than my PS3 and always check my messages. I recieved the credit without knowing since my Vita never showed it. Any reason why?
The credit was only redeemable on the PS3, so it only showed up on the PS3. Not everyone received the credit. It was a PSN "loyalty" reward. It was never clear how Sony defined loyalty to PSN, but signing in on your PS3 regularly was apparently one of the criteria.