‘Quantity reserved’ from the Manual reservation in Maintenace Material Requisition (MMR) lines is only updated after reserving, for quantities reserved by previous MMRs.

Following image shows that even though the quantity available has been reduced there is no place to show the reserved quantity reduced. 

The following image will provide a more explanatory example. Here is a scenario where out of a total of 5 quantities to be reserved, 2 have already been reserved. When you attempt to reserve two more, there is no column to display the already reserved quantity for this MMR. It illustrates what has been reserved previously.

It is beneficial to have a Column to show the already reserved quantity for the current MMR.