Yeah, you're a bit too worried. If it's working now, shrug it off. I personally wouldn't be worried. The cover isn't even on my computer and I'll reach in and molest my video card for shits and giggles.
By the way, old stuff was much more ESD sensitive and a static shock that you feel is in the thousands of volts. So it *is* possible for a shock that you don't feel to damage stuff.
I would fully expect card failure, however.
To put the concerns of the OP to rest though, he could test his card using
FurMark 1.7.0 which would test the core and then use
MemtestG80 which would test the RAM on the card.
I think that should do it...