It doesn't really, unless the founder has signed a stockholder's agreement with other founders or investors specifying a vesting period. Under normal circumstances a founder or founders form a corp, put some cash/equity in, sign a stockholders agreement specifying who owns how much, and from that moment the equity is wholly owned by the signatories to that agreement. Other agreements may come into play as the company seeks additional investment, etc., but I can tell you that at least 20 years ago when I did a startup + angel round + series A + B nobody at any time suggested that the equity I'd worked for the first four years should somehow be clawed back and then vested, and the conversation would not have gone well if they had.
Founders outright own the company in the period between creating the C Corp through taking safes, if any, until taking a priced round.
Depending on the progress at that point, you may or may not get asked to revest. In our case, we negotiated with our VC that our vesting period started on incorporation. However, we were funded within 6 months of incorporation. If that period were to be years, it would be extremely reasonable for a VC to demand revesting, and to the benefit of multiple founders IMO.
