While the steel hubs and steel, cottered crankset are indicative of an entry level model, I have reservations about it being a 1970s. boom era model. Normally, entry level models from this era would have a stamped dropout without hanger and would be lugged construction.

More likley this is an early 1980s model. This was a time when several manufacturers were introducing lugless frames and forged dropouts with integral hangers were filtering down to the entry level models, yet steel components were still fairly common. If we accept that the RS derailleur is an original component, it would seem to corroborate this point of view, as the date code indicates August 1983, suggesting a 1984 model bicycle.

The most reliable indicator to verify the general level of the frame is the seat post diameter, which correlates directly to the grade of tubing employed.

BYW, what makes you think your Mistral is a 1972 model? It looks slightly more modern to me.