Link to Wikipedia:
https://en.wikipedia.org/wiki/Minsk_Automobile_Plant
Link to IMCDb listing:
http://www.imcdb.org/vehicles.php?make=MAZ&model=
autowp.ru is a nice website for factory pictures, but is definitely not a trustworthy source concerning the model years.
Timeline:
1990's
1991 МАZ 6430 Опытный