Here is a perfectly genuine Sporto I own.
However caliber is 2542 that has a production between 1966 and 1969, so technically not from the 70's.
As Zenith moved to the square logo from 1970 not sure we can say that applied star was the standard at that time.
They also use the painted square logo on some watches beween 1970 and 1975. (maybe only for quartz... but not sure)
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