I'm going to guess that
A) you knew that they are polarized like that and
B) you were just so damn excited about installing them you forgot about it.

It's good advice though. I think I would grab a sharpie and trace the path the grnd follow or the VDC. You can see them all at once and you could easily wide any contacts you hit of with a q-tip and some rubbing alcohol.

Good advice though. I bet I forget and do the same damn thing someday...