Setting an 'As at' prompt for assignment data in OTBI

Summary

I would like to be able to set a prompt that will bring back all the assignment data at a given point in time.

Content

I have some reports of worker data (grades, locations etc.) in OTBI and I would like to be able to set a prompt that will bring back all the assignment data at a given point in time. 
E.g. Name, grade, department, location as at 31/07/19.
I have tried linking it to the assignment start and end dates but that limits it to those starting on that date. It doesn't bring back everyone with their data at that date.