How to Date Shakas in the Firth Century B C?

We have traditionally dated that vicramadita, kalidasa and varahamirava in the firth century b c. Because 57 b c was the epoch established by the vikrmati. And you say that shakara commenced in 78, 80, a person who is referring to the epoch of seventyre? How can you date him at least a hundred years before the particular a that epoh commenced it? We had no answer. Then we started rejecting the all. Maybe some errors, ar er brukship,. i don't know what kindof they say interposations are. Even they said that indians had no knowledge of no sense of chronology