Why not natural keys?
RefAtbl <===>> RefBtbl
Columns in RefAtbl... ID; Key = ID
Columns in RefBtbl... ID,OtherNumber; key = (ID+OtherNumber)
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Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.