Easy to ask the nut size, of course, however my '63 is 1 11/16", so I'd assume they didn't go back to a smaller size in subsequent years.
Yeah but Clyde's is a '65 with a 1-5/8".
We saw some mid '80's D30s (or G37s?) with a similar "issue": 3 reported with 1-5/8 nuts (when spec was 1-11/16) within a few s/n's of each other, making me suspect they simply built at least a "run"(loose usage) with 1-5/8 nuts maybe for no other reason than to get some of 'em to market that way.
And early '60's seemed to be a period of wider nut preference, but maybe just did that kind of thing with a run of off-spec nut widths occasionally?.
(There's precedence for doing it
intentionally on an early run, '64 I think, of both D40's and D50's with
1-3/4 nuts and exceptionally flat board radius, too)
From what I can remember seeing here over all the years though, a 25-5/8 scale was most likely to get a 1-11/6 nut while a 24-3/4 scale would more likely get the 1-5/8.
And don't forget to toss in the 32nd inch tolerance on final shaping of the neck.