Validate multiple fields


I have a table Product A, and has a field Serial Number. Then I have another table Product B, which has 5 fields; Product B Serial Number, Product A SN(1), Product A SN(2), Product A SN(3), Product A SN(4). I have 4 connections from Product B to Product A.

Is there a way to validate that each Product A is unique, and no duplicates were accidentally entered, within Product B?