> there's no good way to "auto-format" it even if you knew the issuing PCN of the card before hand. this is plainly wrong. you can swap the mask as soon as you

> there's no good way to "auto-format" it even if you knew the issuing PCN of the card before hand. this is plainly wrong. you can swap the mask as soon as you know it's amex from the prefix. i know because we do it without any issues. it's 4-4-4-4 for visa/mast/disc and amex is 4-6-5. you have more than enough info by 4 digits to choose the correct mask in all cases.