...there really are no rules. The late 1940's/early 1950's was just a very jumbled period for Omega.
Here are some pages from a 1950 Omega Catalog:
Even in this catalog (probably Swiss or French- note the Fr.'s), the reference numbers do not match the nornal Omega references we use today.
Omega wasn't consistent about putting any model names on the dials until the introduction of the Constellation in 1952. Even then, there were variations without model names (like the original Globemasters). Also, some later references were produced with and without the Seamaster name depending on the market.
Generally, I defer to the Omega database if I can't find any information to the contrary,
gatorcpa