Well I wouldn't say zeroed is zeroed. Each person shoots differently, and has slightly difference in POI.
Zeroed is zeroed, until you change the person pulling the trigger. Then, zeroed MIGHT be zeroed, or it might be a bit off.
Shooting from field positions is different than shooting from a bench. All kinds of factors change when different people are shooting the same gun and ammo. Sometimes it makes no practical difference. Sometimes, it does.
He's an example, a friend of mine and I were playing a shooting game. The object was to drive tacks at 100yds. He had a Ruger 77 in .30-06 and I had a Remington .308. Both rifles had 3x9 scopes, and both had been "zeroed" to hit exactly point of aim at 100yds.
We traded rifles after each shot. Shooting was done from field positions, mostly sitting or prone. Interestingly, we were both exactly 1/2" off shooting each other's rifle. And, it was consistent. The amount of difference and the consistency were probably just serendipity, but the point is, each of us, shooting a rifle sighted in for the other guy, neither or us was exactly on target. Noticeable because we were shooting small targets, not deer.
Over the years, I've boresighted many rifles. Many just by eye alone. Some with a collimator. Never used any of the laser gadgets. Always put me on the paper and CLOSE to the point of aim. Final adjustments are always made from shooting results. Lining up the sights with the bore is a good start, but does not guarantee the bullet will hit exactly on the point of aim. Sometimes, it will, and that, too, is serendipity.
As to a "Dirty Harry" gun collection, the OP has done a reasonable job, considering you cannot get the "right" Auto Mag without having it custom made.