As you're already aware. Correct maximum cylinder capacity is measure by pressure@temp. So, the temp of the gas in your tanks can have a very measurable impact on the measured pressure.
It's perfectly normal to see a 200-300 psig decrease in pressure because of the cooling that takes place after the gas has been compressed by the filling of your tank. So, 3200-3300 psig fills are the norm for shops that don't what their clients complaing about only having 2700-2800 when they get to their dive. If a tank is being filled directly from a compressor the reduction in pressure from cooling can be greater.
If by chance, your tank was filled slowly and at a cool temperature, it is certainly possible that with warming you could see a couple hundred psi increase. I've seen tanks read 3000 in the shop, and after getting driven to the boat in the back of a car, placed in again in the direct sun on the back of the boat, when they where finally connected to a regulator they read 3500 psi.
However, I have become highly suspisious of spg's. They aren't particularly accurate to begin with, and live a very hard life of frequent salt water immersion. I've seen three different but otherwise trusted by their owners gauges read a total of 500 psi different on a full tank. I used to wonder why people would invest in a dedicated "tank checker" but now own one.
Bottom line. The highest risk of tank failure is at the time of fill. If you have a shop that gives good fills don't complain. If it let's you sleep easier, bleed your tanks to exactly where you wan't them.
Hope this helps,
