I have had this Kassnar for a long time.  Will post pics later.  Dug it out and noticed the serial number is between 0050-0060.  Earliest serial number I've heard of.  Was bought by an uncle when it first came in.  Still looks new.  All numbers matching except the bolt. Did the early ones not have matching numbered bolts?

It just means that they swapped in another bolt to make the headspace come out right when they were building the rifle in Hungary. As long as it has a number its still a military bolt from a Hungarian service rifle. Same with the barrel - if you remove the gas tube so you can see the top of the barrel, it has many proof marks and a number which probably won't match the other numbers. This is mostly how they came.
Anyway that is a great rifle to have, and we will never see genuine European AK factory rifles that came in completely assembled with the mil barrel again.

everything 1saxman says is correct.