This applies to the A320, but I assume it's the same philosophy:
I despatch with Engine 1 Reverser INOP. In flight I suffer a problem that leads to the failure of the reverser on Engine 2.
I would check the failure in the QRH and it would have both "With Reverse" and "Without Reverse" landing distance factors.
"With Reverse" implies I am using full reverse on all remaining engines (Number 1)
"Without Reverse" implies I do not select reverse.
As you can see, if you dispatch with an engine reverse inop you must use the "Without Reverse" figures because the QRH has no means of knowing which reversers were inop when you dispatched.