Al, this thread has over 240 replies, over 4,500 views and I don't see a single post sharing your interpretation.
When this happens to me I rethink my position.
All that is well and good but evidently the folks in his work area have not posted as his regional ECs and AHJs seem to agree with him. If the real world Al works in has the same interpretation, why would he rethink his position because of a few forum opinions that contradict his real world experience?
Our forum is just a small subset and perhaps Al is giving us a view into an area that has a unique set of circumstances.
That said, I happen to agree with Al that if the existing circuit was ever recognized and allowed as an approved grounding means then we can't later say "my bad" and force an upgrade if it is not being modified. I happen to like his argument that points out the slippery over-reach slope of what that would mean with other code changes.
I am not clear about if BX without strap was ever recognized nationally as a grounding means but Al's area evidently recognized it. I have also seen BX used as a grounding means but unfortunately did not have the awareness at the time to note if all of it was with or without the strap as I have seen both and did not know enough to know if it was a compliant install or not. By the time I started paying attention it was a limited distance on flex.
I will say I do not remember wholesale replacement of old BX unless we were doing a rewire. Never thought about Al's points much till now but I do see where he is coming from.