I think there's no way to know if it's been used so far no?
From what i've heard it would take some serious audits to know the real supply but yeah the chances someone actually spotted this vulnerability in the past are slim.
I do not know if new Zec has been minted, I only posted what I know about the vulnerability, that there has been no explanation. Researchers and Zcash developers have stated that they have not found signs of any exploitation, but I do not know if they were lies and bribery, but I do not think it can be like that.
As they say "don't trust, verify".
It would take more than a statement from Zcash devs for the uncertainty around the coin to go away.
At least an audit by an independent 3rd party firm with good reputation.