RN' also get screwed up since they are Army tracking mechanisms.
Tanks produced new for foreign sales and the USMC wouldn't receive them and would cause serious jumps in the sequence. Many of the early M60's I documented didn't have RN's stamped in the front hull. The ones that did looked like it was done later in life during a rebuild. Most of the Mississippi RN numbers stamped were a much smaller size, about 2/3rds the size of the standard numerals you would find on a later model tank. Coincidentally these tanks all appeared to have gone through a major refurbishment.
What I was meaning was that the later serials may not have been consecutive on a micro scale. For example, S/N 5 through 10 may have been built on the same day but may have rolled off the line as 5, 7, 8, 9, 6, 10.
That I agree with,
Another consideration is that production, weather it be in Detroit or Newark, was dependent on delivery of the cast hulls and turrets from other locations (East Chicago, Pittsburgh, Wheeling, etc). So in theory a thin hull could be a higher number than 20 if delivered late. All thin hulled tanks I've seen were one piece made by General Steel Castings Corporation from Pittsburgh. This would explain why I haven't found any official list of SN's in Army TM's or Memos of these tanks yet. But I really can't believe there isn't one, considering they had to notify units to mark these particular tanks. The most maddening thing is that when these tanks are retired, some have the markings ground off when restored for display. SN 10 at FT Hood is a good example of that. (BTW if your out there Jeff, I'm still waiting to get a good location on her to check out the smooth bore gun).
Still deciphering M60's one at a time.