Here is a Sherpa with the serial number M3C168xx. This Sherpa was originally sold from an in independent bike shop in Alberta.
The serial number is from frame manufacturer Miki in 1983. The component dates confirm the year 1983.
Some people think the serial number might be Merida of Taiwan. The Merida serial number format in 1983 was completely different from the Miki format in 1983, (or 1973).
Here is an RMB Sherpa with a Miki serial number from 1984. From the same bike shop in Alberta. The tubing label says MIKI. Note that it is not a mountain bike.
I do not own either of the above two bicycles.
I have seen another 1984 RMB Sherpa with a West Point Cycles, Vancouver BC sticker. Again, not a mountain bike.
I have seen another 1984 RMB Sherpa with a Miki Sekai label at the bottom of the seat tube.
Other Sherpa brands and models of bicycles:
RMB also had an MTB Sherpa model. I do not know the dates for that model but I am pretty sure that it was after 1984.
Dorado brand in the USA had Sherpa Trail and Sherpa Comp models. Dorado was a brand name sold through Costco.
There is a Sherpa brand name of MTBs in the USA. All of these Sherpa MTBs that I have seen were from Oregon.