I dealt in coins for about 30 years and MT thalers were a standard stock item, coming in and out all the time. As has been mentioned they have been minted at various locations other than the original Vienna, including Birmingham, Bombay, Calcutta, London and other mints I have forgotten.
Contrary to normal practice, collectors often preferred them in somewhat worn condition, believing that these might be "original" ones, although as the design never altered from 1780 I dont know how you could tell an original one from a later strike. Shiny proof versions were struck for the jewellery trade.
One small correction, the standard of silver always was, and remained at, .800 fine