That is verry possilble i think. But i expected higher number of sold turbo-r's .. but maybe they must come.. so .. put your turbo-r serial numbers over here 
That thing was too expensive (today still is) back in 1990~1992.
A friend was there at that time, and he told me they were somewhat difficult to find and when you see them, they were expensive to very expensive.
For the GT price you could get a FM-TOWNS, or X68000, or PC-98, etc. And a LOT departed to X68k or PC-98, since they love new things. FM-TOWNS was a little bit more expensive.
ST: ~$65.000 yen (I don't remember): like USD$ 1k at that time.
GT: $99.800 yen: over US$ 1400 at that time.
Panasonic stopped because not many were begin sold, in Japan they lost the interest for MSX, and Panasonic wanted to depart to 32-bit world (aka 3DO). Until now that story about V9990 begin a project for MSX3 is pure rumour, never trully confirmed, and will never be. We never saw a MSX3 project by Panasonic until now, not even photos, and I could just careless.
Saying the japaneses were still interested on MSX after 1992, is just a "fanatic" declaration (IMHO). 
Retrotechie, good idea, but where you are gonna find´em nowadays? 
By the way, doesn´t anyone here have any japanese MSX´er friends? Who have some sort of MSX forum there? So someone could ask japanese MSX´ers what is the biggest serial numbers they have, instead of us looking over just those very few Turbo Rs what you guys have shipped from Japan. 
Of course it´s nice to see what numbers these shipped Turbo Rs have, but I would like to hear japanese comments too. It was their computer in the past I mean. So they may have some Turbo R stories and facts to tell as well.
Not only the S/N, but country and city as well. 
I bet a ton went to trash, just because the floppy belt went bad.
Also, it wouldn't be a surprise if a lot them came from trash. 
You can find TVs, refrigerators, all things at Japan's trash.
