I have two db's. project.db and earner.db Project db is the main editing screen where you enter the project, you then select the fee earner from the relationship to earner.db who worked on that project.

The issue is this.

I need it to be a checkbox type list so you could select 1, or 2 or more people from earner.db. However, I need the values from earner.db to 1) update for new records but 2) remain as-is for old projects - rather like a lookup.

You need a third file (a so-called join file) linking Projects and Earners

It will have a ProjectID field to create relationships to/from Projects and a EarnerID field to to create relationships to/from Earners; use the relationship from this file to Earners to lookup values from that file