How to restart this letter incrementation based on a condition using Google Sheets Formula?

This formula does increment the letter, but how to make it re-start based on a condition in col A?

=A3&"-"&CHAR(ROWS($1:1)+64)

Here is a test sheet, in case you feel like pouring your blessing: https://docs.google.com/spreadsheets/d/1gh5w0czg2JuoA3i5wPu8_eOpC4Q4TXIRhmUrg53nKMU/edit?usp=sharing

Thanks a lot in advance!