When I was doing the insides I could see little runs of white spots on the tops of the upstairs windows where drips had run down off the frame. If I hadn't gone inside I never would have never have have known.
Although Im trad and at the moment have no experience of WFP, this can happen trad too, although for a different reason, but sometimes errors cannot be seen from the outside, however on inspecting from the insides they become all to apparent.
This is why I question it to myself when guys on here say theyve gone back and inspected the windows and theres no spotting once theyve dried (one particular one yesterday) does that mean theyve checked the windows from the insides?? I doubt it !!
Perhaps its slightly off topic, my apologies for that, maybe it should have been a new thread, but your post did spring this to mind.
Matt