Thanks for the replies. CJ_London, I'm using your solution (as it seemed the simplest). I put the following as a field.
Choose((Month(Date())>=11)+2,Val([cam_sas].[ayr_code]) Between Year(Date())-5 And Year(Date()),Val([cam_sas].[ayr_code]) Between Year(Date())-6 And Year(Date())-1)=True
This...