What's the most efficient solution for this use case ?

What's the most efficient solution for this use case ?

Hi, I'm after an opinion or two about the best practice solution for this problem I may have as my company starts to scale in size. I have an app which I built as a Training database tool. It contains a record of all training available and records what training employees take and when. The employee's manager is able to authorise and monitor their employee's training requirements .. and so far it's working great.

The problem
We are now at a company size, where we are taking on new managers and line management is changing; so the new manager needs to be able to see their new employee's training history.

I created an EmployeeDirectory form/report using the API from Zoho People so that once People is updated with the employee's new manager it updates any associated lookups - but not historical.

Currently the each training record contains the employee and manager (as linked to each zoho user) - what is the best practice for updating all the historical records ?

1) Do I create a function to update all records for employeeX to the new manager ? This would have to be done by manually selecting the variables though...

2) Do I create a new field in the employee form/report that contains some sort of static manager detail and then run a scheduled workflow to compare against the updated field from People, if it differs then do option 1

3) Somthing to do with bilateral relationships ... I've struggled with this as there are several places where the historical records would need to be updated and I just can't get my head round it. Can I have a bilateral relationship between the manager field and several forms ?

I have the same problem in a different app, which we use to track tasks and meetings. There are many forms/reports that have the employee/manager fields in so I would need to apply the above logic, but on a wider set of records.

I hope that makes sense, I can provide more specific examples if it helps clarify