I have one without the dot and it is definitely coated. I'm inclined to follow the day/night school of thought. I would imagine resolution is pretty much the same on all of them with the possible exception that the coating difference (if there is one) may act like a weak filter. I would guess that the film used would have made more difference and maybe the lenses were matched to a particular film type. This does bring up the interesting possibility that the non-dot lenses may actually be more useful as a general purpose lens and suited to most photographers and films.