We have done it several times. We always say the same thing - don't know and won't know unless new data comes to light. Serial number analysis might give a defensible number but not accurate. Many people say more D25's than any other model and I think there is a non-LTG source for that but no details.
I believe that's a reference to pg 12 of the first Guild Gallery, "More D25's have been sold than any other Guild":
When I first saw that back in '97 I assumed it was accurate. In fact I think I was the first person to cite it here.
Since then I've realized Fender itself didn't always have an accurate handle on Guild's history, and 2 issues cloud their ability to make that statement:
A: As has been noted, it's virtually impossible to assign a production figure to them for the years in which s/n's aren't model-specific, (basically all the '70's when one suspects production was breaking new records) unless one has the complete shipping records showing what left Westerly. I'm not even sure Hans has complete records, can't recall if he ever mentioned it.
B: Beginning at some point in '94 D4's and D25's actually used the same s/n sequence, one cannot tell which is which by s/n without the guitar in hand so s/n records are useless for that period as well.
I doubt very much Fender invested the time to vet the shipping records to obtain actual numbers shipped, still, the sheer volume of s/n's that can be tracked shows that the D25 was a production staple and I suspect Fender's claims are actually true. And maybe they included D4 sales in there, too.
Since the D25 was dropped from US production in '04, it
is possible that its sales volume has been overtaken by another model, but given the substantial shrink in production volume after close of Westerly, I doubt it.
In the end only Hans could answer that, and only if he actually has the complete Westerly and Corona production(shipping) records.