I opted to add additional logging to the messageStack functions themselves to see if the add() and output() methods were returning useful data. I used the following statement to output the arrays where the messages were being stored (in the respective functions):

error_log(print_r($theAlert, true), 0);

error_log(print_r($output, true), 0);

So, indeed I was getting the correct array information and errors were being logged (error_log writes to your /cache directory at this point). That led me immediately to the tpl_message_stack_default.php file in which I had commented out the return logic so that the client would be happy while Authorize net was in testing mode.

Removed my local copy of the edited file and error messages are now appearing. Fantastic.

Likely doing a diff comparison of the entire directories would have eventually led me to this conclusion.

Thanks much Dr. Byte

Patrick