The other thing to remember is that even those long-standing institutions had internal change that was a huge deal at the time but is now hardly remembered at all, or considered minor.

You can even see this right now, where countries do not consider themselves to be as old as the current government's age, but much older. For example, most Italians will not consider Italy to be "started" at the Republic in '46, or even the Unification in 1861, but that the country is much, much older.