I mean, take USA for example, is it even the same country after each amendment? After a Civil War? Civil Rights Movement? Landmark Court Rullings?
One could argue that Modern America began in 1965, with the passing of the Civil Rights Act. Or in 2001 when the Patriot Act was passed. Or in 2009 with Citizens United Court Ruling. Or in January 2017 when… you know. Or in January 2025.
When did the country really start?
That’s a nice situation: you see, the answer is completely unimportant and affects nothing. So you can use whatever answer fits your set of arbitrary criteria. You want to show that the country is old? Use the first mention of the name. Very industrious? Use factories per mountain formula, etc…