Some of the black short A6 tubes have required shims to work. The tube threads fit, but they are too short to complete the electrical contact. Example Shim.
I don’t recall any complaints on any of the EE tubes.
As to why the problem persists, my conjecture is that the Customer Service department has no way of communicating such problems with manufacturing, marketing, and sales departments. They are act like a “closed box”, solving customer complaints with their limited tools, with no input into any other areas.