Why won't department names update on positions?

Summary:

Updating department names does not register on positions with earlier start dates than the start date of the name changed on department - why not?

Content (required):

When we change a department name from a specific date, for instance 01/11/2021, this change of department name won't reflect on the positions that are placed in said departments.

Please see attached screenshots. The position may have an earlier start date (very far back in this example), but why does this block the department name from being correctly updated? How can we fix this without having to create a new time period on the position?