You didn't post a full shot of the back, but I'm betting it doesn't have a full-width bumper on it but has the earlier split ones. If that's the case, it is possible that the car was in an accident (possibly very early in it's life) and it was deemed easier to repair by grafting on the bits from a later car (more parts available than earlier cars). Or, as has already been suggested, the chassis could have been set aside and finished much later than the normal VIN sequence. The latter seems less likely given the amount of time it would have sat to get finished with the larger front bumper. Either way, I see no impact (upwards anyway) on value with the later bumpers. It's not like a '71 Hemi Cuda where people go bonkers when it was one of two orange cars ordered with a tach, a glove-box cup-holder AND the passenger-side mirror option...
Mark