I've taken the .625 wall test for Exelon Nuclear and they only certify based on nominal thickness... Yes in theory, .500 qualifies you for unlimited, but if you go by NPS, the NPS could be .600 and your GTAW deposit thickness is .125, then your SMAW would be .475. Also the big thing is, Exelon doesn't re-up your certs when you weld for a participating contractor...They're only playing half the ball game. They'll cert. you at the union hall, you'll have them for 6 months and then almost every time you go to weld at a nuclear site, you have to take qualification test again.
Regards,
John