Allow creation of new records through relationships without affecting exisiting records?
I am building a database in which I have a few different tables which I need to reference and input data from one central table. I have auto lookups on my main table for each related table using the automatically generated serial number for the respective records. Everything works well until I need to add a new record. Because the auto-enter serial is setup creating a new record works great, but If I forget to erase an existing serial number from the "serial's cell" prior to typing in another cell, instead of creating a new record it changes the current record related to that serial number.
Is there a way to keep the existing lookup, auto-fill and record creation infrastructure while not allowing it to change already existing records' information?