This is a very interesting topic. In the overview below, I arranged the dials in order of appearance (1979 - 1983). Please let me know what you think and which dial variation is considered which mark. The dials in the second row appear to be slight variations of the ones in the first row (bolder/thinner prints).
Also, check the area where the f of feet meets the v of Superlative. This could be an easy way to tell them appart.
a) 6,4 million
b) 7,1 million
c) 7,2 million (8,3)
d) 8,2 million
Cheers
Jose Pereztroika