Except the 1928 law and the 1938 laws were passed by rather different legislatures.
The 1938 law deregulated gun ownership for almost everyone except for the Jewish people. Even those people whose ownership wasn't as free as those organizations mentioned above had their access to firearms increased. Also the 1928 law was a LOOSENING of the 1919 law by the very source you reference.
So actually the first thing the nazis started doing when they took power was to give guns back to most of the people.