Confirm zero when possible...
Before optics (and those were usually bought out of pocket personally) I remember when the M16A2 came out and that big knob on the rear sight windage adjustment was new from the old flush steel ring with holes in it and a detent button. Sure it was more precise and easy to set on the range and go qualify but damn that thing was always getting bumped, snagged on uniform or whatever and spun in one direction or the other. You had to always either look at the hash marks or prepare (reset) prior to movement or after airborne infil to know if it got bumped off zero.
They still used that on the M4 and most aftermarket companies still use today for BUIS.
JMHO but LEOS and Feds should be shooting enough every quarter that what they have is recently zeroed to seasonal weather. Problem is storage in the extremes - frozen or burning up in the trunk of a car when needed. Makes me think good old iron sights would be best. Soldiers and those that fly into remote higher or lower locations from base camp with 40+/- degree temperature changes would benefit too from going old school even though it's not tacticool.
Iron sights never failed me...well until this past Wednesday when I pulled my service pistol out in the range and the seven yard warm up drill prior to a qual was, well, not where the bullets should have been hitting the center of the circle I was aiming at. Brand spanking new Sig 229 so f'd up now because the agency screwed Sig over that they have ruined a great gun. Oh what was my problem. You can move the dove tailed front sight post 2mm back in forth by hand. At 15-yards that's enough in one direction to shoot bullseye and pushed over the other way a good five to six inches to the left.
I miss my old gun. Nothing wrong with it just lots of rounds fired and seven years. Worked fine! Had a SRT and big dot tridium sights; can't put an SRT on the new gun that's how messed up Sig is. They have become Kimber quality.
Sorry for the rant...now where was I? Oh optics and extreme temperatures. Never had much luck with frozen batteries and I hate super hot places.
Tennessee elevation and Kentucky windage! Learn it know it. When bullets start flying and you ain't hitting what you're aiming at you better quickly figure out what you are hitting and adjust fire!