Thank you so much for a rapid answer. With no background into the history of the language, I would not have known where to look for this sort of thing.
I see now in Dyalog's "Mastering Dyalog APL, 1st Ed.", ~p372 "Specialists Section" there are discussions about this and related language differences.
There are a few items to digest there in regards to their ⎕ML System Variable and how it handles APL2 (IBM) vs. Dyalog APL dialects.
The more I explore, the more I question whether I must choose to study "the APL2 path" or "the Dyalog APL path" ... :) I hope I do not have to choose!
So far, trying both dialects while learning has illuminated some concepts for me, but I fear I might confuse myself with implementation differences.
Again, thank you very much for the insight.
-Russ