Does a visa extension count towards the 90 days? [closed]

We arrived in Greece on December 17, 2017. Our 90 days were up in March, but we were granted a type C visa extension to remain in Greece through June (refitting our sailboat).

Does this extension count towards the 90/180 rule or are we free to sail on to Italy in June? We are US citizens.

Thanks for the help. We've googled around and haven't found an answer.