BillYo414 - I realize that what I'm about to say doesn't really answer the question you've raised, but I'd be interested in hearing your thoughts.
I also own a CAB-1L and initially found a paragraph on page 9 of the Owner's Manual for #6-37147 (the CAB-1L & BASE-1L combined set) quite interesting - recognizing that TMCC engines do not have Quilling whistles anyway. Briefly, point #3 describes the procedure "to toggle the whistle configuration between TMCC1 and Legacy style for the current engine or train." It ends by referring to the 1 or 2 beep meaning.
Quite frankly I've alternated between the 1 and 2 beeps from time to time but really haven't noticed any substantial difference and, when reading your Post, wondered if you have?