FWIW, the bike ADB used for their '84 125 MX shoot out had a shock like that. Neither of the 125Ls I've owned have had that type of shock.
The BASS crap was - in Australia - 85, 86 (and 87?) only - definitely not an Aussie 84 shock.
I reckon your JDM vs export model theory is probably right. I'm told by a pedantic source that the JDM YZ-Ls had front discs, which also supports the idea.