Btw, the Yachting Journal has a pretty extensive database of Hatteras yachts ...
https://www.yachtingjournal.com/directory/boats/builder-hat
You can filter by size and year (and state). I pulled about 35 hull numbers (AM series, 53 MY) from 1973 to 1988 and plotted them out. They appear to be both sequential and incremental.
The number of 53's sold per year varied. They sold modestly in the early 70's and then accelerated in the later 70's, through 1980, and then tapered off again. It seems that they built around 250 of the AM series, with about half of them being built during that 6 year boom. The lowest hull number I found was 404 in 1973 and the highest was 649 in 1988. I realize that a few were built before 1973 and a few after 1988, but if you look at the yearly production numbers, there weren't many.
I know that the number 349 was thrown out there for 53 MY units, but does that also include the ED models?