If you take it for a drive to the panelbeater now, he can probably show you where else it's going to break out.
Do a VIN Fast to see where its likely home was in Japan.
If the car came from a winter snowbound area, the future rust is likely to be under the car especially in line with the wheels. If it's from a coastal area, surface rust can be anywhere on the car with deep-seated rust coming through too. Ask the panelbeater for use of his paint thickness gauge. You can only measure on metal areas. On top of the body it should show above 90 microns. Undercarriage; if it's below 50 microns, it'll explain why Evos or all Lancers might be prone to some surface rust. Anyway, have you tapped away with the screwdriver yet?