It’s interesting if not confusing. The difference between V2 & V4 is that V4 uses the credentials generated from an IAM identity and has a set of 2 credentials compared to a set of 3 for V2. The email I received told me that after the October deadline, V2 would be throttled rather than blocked. That seems to be the case since our email has continued to operate. Another difference in my case is that I don’t use AuthAWS with V2.
Anyway, I will try the same test code with the later version and report what happens.