Note the small gap between the cap and the nozzle
The answer turned up quite accidentally after I had purchased a five pack of glue for Au$2.00. Not expecting a quality product at that price I was prepared to chuck a tube away each month regardless of how many times it was used. One tube I opened had a rough edge on the open end of the cap, the result of poor moulding, and when the cap was tightened there was a bit of a jagged edge sticking out. This I trimmed off with a modeller's knife. After that, I noticed that when I opened the glue there was a flat 'flange' of glue on the nozzle each time I opened it. Each time I used the glue I wiped the end and screwed the cap back on. This tube of glue survived for several months and was only discarded once it was empty!!??
Small flange on the end of the nozzle where the cap now seals it!
The theory as I see it is that the cap does not cover the end of the nozzle when in place, thereby allowing the tube to 'ventilate'. By trimming off about one millimeter I have allowed the cap to seal the end of the nozzle, hence the 'flange' formation when the cap is removed. Also, when I use superglue I never squeeze the glue out in an upwards direction. This very quickly expels the air gap in the tube that the glue needs to stay liquid. I always invert the glue and shake it once to get the liquid into the nozzle. Still holding it upside down, I squeeze out the desired amount. This retains the air pocket in the tube.
The tube 'at rest' between usage
I don't store it in the fridge or under the stairs or in the bottom of the fish tank. It sits on my workbench in the garage summer and winter and survives temperatures from 5C to sometimes as much as 35C. Once finished with, I 'nip' the cap back on and store it vertically in a small drill stand I have, knowing full well that when I go back to it in three or six months time, it will still be fine......and it is!!