When I say wipe out everything, I meant everything in the game folder, not my browser cache.
Overwrites will happen only if there is exactly the same number of files and with same names
I do this because Construct creates sprite sheets and gives them names without my input. It is possible that a different export will have more,fewer and/or differently named sprite sheets, so if your javascript files do not all update you get code pointing to a sprite sheet that is still there from the old version and a screen that makes no sense ( random sprites all over the place )
So just to be safe, delete everything, then opload the new export