The -V variant gained the Viper callsign. I don’t think it’s correct to call anything before F-16V “viper.”

Unlike many other military aircraft, Wikipedia does not have a complete accounting of every F16 in service–merely saying “4,500+”. So it’s a fair guess that there are still some non-Viper Falcons knocking about somewhere.

Although officially named “Fighting Falcon”, the aircraft is more commonly known by the nickname “Viper”.

From Wikipedia.

I stand corrected, apparently both nicknames are in use.