The Mellotron Group

Would Martin or anyone at the factory know?  Is there a serial number dating guide for Mellotrons? Never even thought to look for one til now.  Mine is #1485, not that much later.  Bought it used, of course, but I was told only "Early-'70s," which made sense. It was pretty much showroom clean, so it wasn't old & beaten up.  I bought it around mid-late 1976 to early 1977, from a fellow in North Hollywood, CA.  (I'm shocked I don't remember the exact date & time!!)