so is this a bumper made for a 1968 but manufactured in 1973?
That would my opinion based on looking and documenting a fair numbers of this. Could be manufactured in 1983. Don't think they were stamping service replacements in 1993
Later bumpers can be found using a different date pattern where the year is stamped using the last two digits of the year such as "73" for 1973. Just more room for more letters and numbers built into those stamping dies
Have not worked out all the patterns for all the bumper patterns I have pictures of. And of course as with sheet metal we do find mistakes though these should be seen as rare cases but even they form patterns that can be applied and tracked along with the others