The "Boeing Statement on AOA Disagree Alert" tells us that the MAX has had an AoA disagree alert function from the outset, but in error, it was not displaying to the aircrew. There is a long and convoluted explanation/justification of why that deficiency may not have been critical.
Lets not be distracted by that argument. The real issue is that if the AoA disagree signal system was available " in keeping with Boeing’s fundamental design philosophy of retaining commonality with the 737NG" why on earth was it not used as a critical input to the MCAS activation logic ??