Generate item code with a sequence based in an EFF value

Summary:

Hi there. We would like to generate an automatic item code using item code rules with the following logic:

Each item has values in EFF A, B, C, D, E + correlative

Then, we want to generate the item code concatenating ABCD and at the end, generate a correlative based in the combination of existing values of A+E.

We know how to concatenate, nad we know to generate a correlative based in the value of ONE EFF, but not based in the combination of two.

Example:

A=23; E= FGG ---> correlative = 1 for EVERY item with this combination of A and E, no matter the other values in B,C,D.