A repair is only invisible if the refinish is. Matching is done against the panels either side of the repair, because paint on a car that has been outside for years is not the color it left the factory as.
Most of the time in a refinish is spent before any color is applied. Surface preparation is what decides whether the finish is still there in three years.
Colour is carried into the adjoining panels rather than stopped at a hard edge, so there is no line where the repair begins.
Not every job is a repair. If you want the whole car done, that is a conversation about condition and expectations before it is a price.
Rust that is filled and painted comes back, usually within a year and usually worse, because the corrosion underneath never stopped. Affected metal is cut back to sound material and replaced. It starts in wheel arches, rockers, the lower edges of doors, and anywhere a previous repair trapped moisture behind a panel. Rust in a load-bearing area is a structural question rather than a cosmetic one, and gets treated as such.
If it has been hit and it also needs mechanical work, it does not need to go anywhere else.