There’s a base default, for games that don’t have a valve default. Devs can also set a default themselves IIRC which is essentially the same as a valve default for the purposes of this conversation. The original implementation did not automatically allow all games without a valve default to be run, something that there’s still a setting for which is now default on. The override option overrides either the valve default if there is one or the base default if both the option to allow games without valve defaults is on and there is no valve default.
So if you override a game that does have a valve default and then remove the override, it’ll use the valve default whatever that happens to be at the time.
There’s a base default, for games that don’t have a valve default. Devs can also set a default themselves IIRC which is essentially the same as a valve default for the purposes of this conversation. The original implementation did not automatically allow all games without a valve default to be run, something that there’s still a setting for which is now default on. The override option overrides either the valve default if there is one or the base default if both the option to allow games without valve defaults is on and there is no valve default.
So if you override a game that does have a valve default and then remove the override, it’ll use the valve default whatever that happens to be at the time.