Record a date in deadline field when resource management is on


Hello all

I have a request form that works great and I am using it for resource management as well. This means I have start date, deadline and duration.

Initially when I receive a request I manually put the start date and deadline. Sometime my team finishes a task "early" and the workload will still show up in their report. I would like to fix this so I tought "let's just record the completion date in the deadline field"

Problem: I cannot do that, and it seems it is because I am using this field for the workload.

Can someone confirm this is why it's not working? Does anybody have a workaround? The only I can think of is manually change the deadline after the fact, but I would prefer something automatic obviously.

Here are the field I am able to use. I am not using "Expected delivery date" anymore but it's here for old records and I am currently using "Actual delivery date" to record the completion. I'd like to record it in the "Deadline" field.