Warn users if there are saved records with the same claim number

Hi, the claim number should not be Unique as it is possible to have multiple records with the same claim number. However for each record we have a field called "decision". If the decision is pended I want people to edit the saved record with pended decision. if the decision is accepted then it is ok to create a new record with the same claim number. How can we let users know if there are records with the same claim ID but pended while they are creating a record?