One more and don't tell me this doesn't happen

Go through the whole drymount trimming mat backboard frame thing, looked at glass/poly from all angles. Slide it all together. Scan every square inch quick but separate, then put the cap on. Put it on the wall, deliver it, whatever. That piece of paper is sealed and in the can. And a year later, down in the corner is a mosquito. There is positive pressure on every periphery. Nothing can get in. But there is the mosquito. Or gnat, or whatever. Open to speculations.

I can't tell from the above what your actual frame is in this scenario (if there is one). Flex/movement due to temp/humidity and the little bugger gets into the gap?

I once watched someone in Purgatory trying to spot out the silhouette of a mosquito which landed on a sheet of film after it got inside the bellows and decided to land there. It was a relatively well known Alaska shot by Ansel Adams, and with the amount of enlargement involved, the mosquito impression looked the size of a wierd alien spacecraft about to land.

Unless you know how to actually hermetically seal a picture frame sandwich after vacuuming the air out (tricky and expensive), conspiratorial bugs can sometimes find their way in. Maybe cover the framed print with mosquito netting? That would be novel.

Welcome to framing. Try taping the package with scotch tape (3M Magic 810) first before dropping into frame.

I am talking positive pressure on the periphery, all sides. Yet, there it is. And not only that one but others. Not only my prints. Went to this show in Vancouver and I saw a bug behind glass. Made me feel better about my own presentation. Bug is now feature.

There has long been a custom of gluing down a sheet of impervious paper onto the entire back of a frame, supplementary to the internal picture backing. But that doesn't help much if something gets trapped in first. Professional framers call those little annoying anomalies "fish", like fish swimming around behind the glass in an aquarium, even if those "fish" are actually bugs. Tiny booklice (Corrodentia) are really hard to keep out if any kind of dextrin glue is involved; they feed upon it.