Here's some information that I hope will clarify the confusion US Market Plus 2 VINs. For background, I own 2 Lotus Elan +2s: a 1967 +2 (050/0164) and a 1972 +2S/130 *72010239N).
The first thing to note, is that all Lotus Elan +2s are Lotus Type 50s.
As was noted earlier, the pre-1970 Lotus Unit Numbers were composed of the type number/production number, thus my 1967 +2 is identified as the 164th Lotus Type 50.
This format was changed as of 1.01.1970 so that the VIN/Unit Number contained the year, month, batch and production number with a letter (YYMMBBXXXXL). Thus my +2S/130 was built in January 1972 and it was the 239th "N" unit produced. The batch number had been discontinued by this time. While the Type No. does not appear directly, it is coded in the suffix letter "N".
By adding the letter to the unit number, Lotus identified both the Type Number and the destination of the unit. Suffix "N" indicates that the unit is a Federal (USA) Market +2S, while a+2S with suffix "L" indicates that it built for the UK Market and an "M" suffix indicates it was for Export (to Other Territories).
So Tom, please be assured that your +2S is in fact a Lotus Type 50, as indicated by the "N" and the other numbers that are in support.
You mentioned that you looked at another +2S that had a identification number that started with "36" rather than "50". I believe what you were looking at was the lubrication plate that has Lotus Part No. 36B1135. I'll try to send a photo of my plate that shows this.
Happy Lotusing in your +2S...
RR Shetler