If you have one parent list (which you need for a constructed list), then your codes will always be the same in the data file regardless of the order you put them in for the constructed list. It maintains the codes based on the parent list. Can you post your constructed list code? I'm sure its just a minor typo or syntax problem. Make sure you are using the exact names of the lists or variables, Perl is case sensitive.
As an example, if your parent list was called "Brands" and the REGION you wanted to have the extra 3 brands (we'll say 1, 3, and 5) was REGION 3, you would have something like this.
Begin Unverified Perl
if (VALUE("REGION") != 3)