Lock in historical values on a visual

Hey All,

Have a question regarding creating visual where historical values don't change. I'm trying to see workers that haven't worked for 3 months and report this number weekly/monthly. Naturally these workers may get a job and would drop out of this number, but the visual I want to create should not have the number change. For example, if for April there were 5 workers who didn't work, but in May, 2 of these workers were rostered to jobs, the number showing should still be 5. 

There are 2 tables being used for this, Workers and jobs. How would i create a measure that i can use in a bar chart that can lock in historical values?

Thanks in advance!