I open ammunition boxes all the time, including sealed ones, old ones, scarce ones. There is ab solutely no scholarly reason for keeping a box full - nothing is learned from a full box that is not learned from a box with one original round still in it, unless the box was packed with mixed lots or headstamps. I subscribed to the notion that it is somehow a sin or dumb to open boxes, a lot of collections would have fewer good rounds in them, including mine, probably. I would have 16 rounds of German 9mm WWII Stahlhelmabnahme Patronen (Steel helmet test loades with yellow lacquered case mouth and primer seals) and 14 other collections would have not have them. But wow, I could say I have a full box! Sorry, can’t see the sense to it. If one keeps them just so they can sell them later at a big price to someone else who thinks a full box is the cat’s meow, that’s o.k. We each approach collecting in our way.
Further, you have a nice old box, full to the gills and never opened. Oops! Dropped it on the concrete floor. Now I have the remains of a full box, split at every joint, that I can glue back together. But that’s o.k., I didn’t open that sealed box myself (least you laugh, guys, this happened to me with a beautiful full box of old Winchester 44 WCF I had with one of my 73 Winchesters. Now no one has it. It was so split and torn, I threw the remains away as I recall.
If I drop one of my boxes with one round in it, I bend over and pick it up, dust it off, and put it back in my cabinet unharmed.
I won’t say I’m sorry. If I get another full, old, rare box tomorrow and want to examine the cartridges in it to learn something about them, or simply to pass them around to my collector friends, I will get out the razor blade in a split second and start cutting!
By the way, you never know when you will find something in a full sealed box that by everything the label says, shouldn’t be in there. Not that it was an important find for rarity, but I identified a Greek clandestine headstamp years ago because there was one miixed in with standard Greek headstamps (identical cartridge characteristics) of the same date in the box.
Don’t bother to nail me to the cross on this answer. It won’t change my mind about doing what I do, or of the lack of any necessity in the study of ammunition to keep a box full.