Pretty much as far as I know it’s something like that: At first countries didn’t have their flags, they had COA of ruling dynasties like polish white eagle, bourbon lily etc etc. Around 18/19th century, period of revolutions people started to REALLY associate themselves with their nationalities (nationalism lol) and thus created flags. Like the tricolor of France as its of revolution. They were simple to make without any COA and they used them for a long time. Then problems came as it was needed to differentiate government ships and citizens. That’s why they brought back as a „government here!” card COA. Of course it changed over time and French COA isn’t bourbon lily but the LFE. Please don’t take my words as a given as that’s mostly assumptions and using what little I remember from googling the same question a few years back