oil pressure switch threads are different on earlier type. I don't know what year they changed.
During the '69 model year.
The very first triples, although officially always '69, were built from calendar June 1968 - aiui so every US Triumph and BSA dealer would have at least one triple on their showroom floor on the September 1968 launch date.
Early triples have a pressure switch threaded 1/8"NPT (National Pipe Tapered); their part number was D1943.
Twins weren't fitted with pressure switches 'til the start of the '69 model year (there are several other changes at the same time - tacho. gearbox mounting thread from BSF right-hand to UNF left-hand, several other engine threads from British Standard to Unified, blah).
According to the parts books, all twins were fitted with the first of the two 1/8"NPS (National Pipe Straight) thread switches - part number D2133.
In reality, they weren't - my T100 is from the early '69 batch still numbered in the pre-'69 format (H-prefixed number) and the timing cover thread is 1/8"NPT. There was also a batch of early '69 650's numbered "pre-'69" (DU-prefixed number) but I can't be certain whether their timing covers were Taper- or Straight-thread or a mixture.
However, fwiw I am 99% certain all twins built after October 1968 with date-code format numbers had D2133 Straight-thread switches/timing covers originally.
I don't know why some early '69 twins have Taper-thread switches (and timing covers), when the two switches had different part numbers. However, speculating, I wonder if it was a supply problem? All '69 Triumph and BSA models have a hole for an OP switch, but the '69 singles' are filled with a (1/8"NPT) plug; for such an important component in production, they're single-source, from Smiths; triples were changed to a Straight-thread switch during '69; the singles finally got the - Straight-thread - switch from '70.
Aside, it seems the early '69 confusion between twins' parts books and reality, coupled with Meriden's habit of never putting thread details in parts books, is at least one reason why the Taper-thread switch is now supplied under the D2133/60-2133 part number; although, as I say, it was originally a Straight-thread switch.