"new" or "renewal" are semantics; the reality is that every issuance is a new cert.
The concept of "renewing" is only for the human benefit of understanding the process.
So when you get a new cert to replace an old cert, humans like to say it was "renewed".
But it is still completely new and has absolutely no ties to any previous ones.
It's nothing like a parking meter where when your time is running out you simply add more coins to extend your use time.
Think of a cert as a timestamped and bound "contract", "license", or "lease", much more like a "CD", "annuity" or "deed" than a "rental agreement". Any "change" to such would require a new one.
Just for any other readers' reference (and to be 100% clear): There is absolutely no way to modify a cert once it is issued, so they are never extended nor altered in any way.