I believe what you're saying, but it most certainly isn't the norm, in my experience, as well as thousands of shooters in Canada with Swede Mausers with mismatched bolts.
When they were still available, I purchased a dozen NOS replacement bolts so I could modify them to clear scopes on some of the builds coming up. It mostly wasn't a problem because the jobs required rebarreling, and headspace was set during that process, including reaming to the cartridge involved.
However, several of those jobs just involved replacing the existing bolts to clear the scope diopter bell.
There weren't any issues on any of the rifles I swapped the bolts on. These latter rifles were not built on surplus actions, but commercial offerings.
OP, if you're concerned about headspace, the first question is, do you load your cartridges, or do you exclusively use commercial rounds?
If you load your own, fireforming the rounds to fit your new system will take care of everything, once you've adjusted your sizing dies accordingly.
If you're shooting commercial rounds, shoot one and check it for stretch. I seriously doubt you will suffer a case head separation on factory built ammunition, unless there is an extreme condition.
If you're worried about an extreme condition, take a cartridge, apply a couple of pieces of scotch tape over the base, and trim the tape to contour.
Find a safe place to chamber the cartridge and close the bolt. If the bolt closes with some resistance, you're good to go.
The biggest issue with over max headspace, unless it's extreme, is accuracy deterioration, because of the inconsistencies created, by the base of the cartridge being held by the extractor claw, instead of resting in a null spot in the chamber, which can cause inconsistent strikes on the primer and other issues as the case fireforms to the chamber, which has an effect on the pressure curve created during firing.
