We've upgraded the (mirrored !) dataservers first, and then one by one the application servers on a live system (200 msg/s) without any issues

It is an interesting exercise, but what is the point of it ?

And there, my friend, we differ completely. ;-)
"someone made the decision to return a status value from methods to indicate success/failure."
A brilliant idea! (Joe D. ?)
In my code I don't want to catch anything, I want to know if a certain method/function did what it supposed to do and if not: report tat to me in a polite fashion (%Status).