Inner caseback is stamped "5512 III.69." That's period-correct but of course not model-correct. I was told that Rolex sometimes used "5512" casebacks as replacements for 1680 casebacks, but supposedly those 5512 replacements didn't have date codes. I doubt this was the caseback that Rolex originally used for this 1680, but who knows?
Also, I like that this still has the Triplock crown and wasn't replaced with a Twinlock. That's pretty cool to me, even though nobody else seems to care about that particular detail.