I think in general everything mentioned is just the way it is. That is how they built drums. They are not up to the current exacting science that has come into the drum building business.
You will find all kinds of differences and discrepencies from one drum to the next. Many companies just did what they had to and used parts as they came in from suppliers. If the supplier changed then they just went with it and things were changed.
We have many examples of drums that should not be, or should not have been or supposedly never existed. I think many collectors look over the finer details and just want a drum in great shape with no extra holes!
It is well documented that drum badges were not used systematically and if they had parts they would use them up to clear out inventory. Old parts were kept on hand for special order and repairs and eventually used years later to clear out inventory.
So I think many of us including myself overlook most of the minute issues and chalk it up to the manufacturing process of the time.
In regards to the thread issue, it would be something that I would never even consider or document. I don't think there is an answer other then it is just they way they built drums.
With that said, I'm not saying they were low quality, in fact they were built well with quality materials, it just was not cost affective to pour extra labor into making them each perfect.
Hope that helps
David