I just found a response to my query:
"The only way any application can display information is if it is programmed into hardware.. Asus does not program the mainboard serial number into the BIOS.. so all you see in 3rd party applications ia a placeholder."
It is curious two different 3rd party applications use the same "placeholder" as their own application. I've asked if others with my MOBO get the same results.
Asus does not program the mainboard serial number into the BIOS
I called Asus today and got that same answer.
When I told him that the serial no. is shown in Asus Suite, but it's wrong, he had no clue.
He checked and came back and said "the serial no. in system info in the Suite is the Chipset serial no. (although he didn't know why it didn't say that wasn't the MOBO no.)
All, in all, pretty much a waste of time - courteous,though.