I'm guessing there are some cryptographic keys included in the installation that requires updating once every N days, and if it doesn't, it's unable to validate

I'm guessing there are some cryptographic keys included in the installation that requires updating once every N days, and if it doesn't, it's unable to validate new updates somehow. "Evergreen" when it comes to browsers just means that they try to update themselves rather than letting the OS handle the process, it doesn't mean it's always successful :)