Acoustic Guitar Construction

Okee-dokey. I should have provided a better pic to begin with :-)

Looks to my eyes that the purfling channel on the inside is cut wider (smaller diameter) for a bit, and that allowed the outer rings to pull inwards into the channel, leaving a gap at the outer ring when everything's snug to the inside. For what it's worth (zero) I agree that some dark filler cures the problem enough to continue. Appears to me that the outer lip of the binding channel is nice and circular, and that's enough to allow the eye to relax; there's the expected symmetry of the circle.

Dark it will be!

I agree. Dark fill and you'll have to look hard to see it. I did that on a binding gap.

Dark fill worked really well.
Tom is somewhat detail-oriented. Okay, like me, he obsesses about certain things. Like he spotted a little glue inside the guitar and he was ON IT! :-)
The sound port makes it all so easy to see in there.