Suzuki's internal model code for the T500 was 150, and the total production was perhaps 95,000 machines. Using material published by Suzuki, material printed in Mick Walker's book 'Suzuki Production Motorcycles 1952-1980' and input from owners, the production numbers by year appear to be something like the following:
Mark I initially sold in 1968
Initial frame T500-10001 and the final frame is possibly T500-16038 (source Mick Walker's book "Suzuki Production Motorcycles 1952-1980", page 94)
Initial engine T500-10001
Mark II generally sold in 1969
Frame T500-20001 (source - Japanese domestic market parts manual shown to the right - just 'click' on the image for a larger version). Note that Suzuki ordered the photos incorrectly in the manual and swapped the MK II and MK III images - the contents of the parts manual are correct. Mick Walker gives a starting number of 20938 (page 94) which seems unlikely and I suspect it is a typo.
Mark III generally sold in 1970
Frame T500-23940 per Suzuki, or T500-23938 as given by Mick Walker (page 94)
Engine T500-23940, or T500-23980 per Mick Walker
The MK III was the lowest production model and is therefore relatively rare.
1971 R model
Frame T500-31295 per Mick Walker (page 94), or T500-30846 per Suzuki Canada, service bulletin 07-03.
Engine T500-31295 per Mick Walker
Note - in the Japanese domestic market, this was called the GT500 and the first frame is shown as being T500-37225. Refer to the copy from the parts manual above right. The last JDM machine (per other JDM parts manuals) appears to have been T500-51588.The GT500 is not shown in the JDM sales material I have for 1974 onwards.
1972 J model
Frame T500-46463 per Suzuki Canada, service bulletin 07-03.
1973 K model
Frame T500-59779 per the Suzuki 'Model Identification Chart' shown to the right (yes - it is an eye test) and also the Suzuki Canada listing.
1974 L model
Frame T500-68083 per the Suzuki 'Model Identification Chart' and also the Suzuki Canada listing.
1975 M model
Frame T500-74198 per the Suzuki 'Model Identification Chart'and also the Suzuki Canada listing.
1976 A model
Frame T500-90729, re-badged now for export market as GT500, per the Suzuki 'Model Identification Chart' and also the Suzuki Canada listing.
1977 B model
Frame T500-104422 per the Suzuki 'Model Identification Chart' and also the Suzuki Canada listing. The highest frame number noted to date is T500-106884.
Engine T500-104426. The highest engine number recorded to date is T500-108082 (F. Sauter)