fender was a company who wouldnt waste anything, so if they ran out of bf plates and they had sf ones, then they would use em. there are '68 amps that have '67 and even '66 trannys or pots and things, nothing is wasted, so if they found a stash of older stuff, it goes right into the line to be used. is it possible there are some late '67 sf plates out there? sure. ive never seen one and '68 was the official roll out for most of the line with the drip edge. the circuits didnt change much if at all the first few years.