REF ((X,N) function in the Mac language is null when N>=600

Hello, I found in the retest that the function REF ((X,N) is null when N>=600, which causes my policy to fail to trigger the equilibrium condition (I use REF ((H,BARSBK) in my policy, which fails to be equilibrated when BARSBK>=600, because it is null), can this function be upgraded without limiting N?