When is this a problem?
All lists should have a code.
Why is this a problem?
A code makes loading and using a list more efficient, so it is best practice to include a code, especially for numbered lists.
How to correct:
Check source system availability for creating a source code, as this is often possible. If not, you can use Anaplan to create a code.
More information:
Creating Codes for Attributes
String Concatenation
Questions on this topic? See Does the list have a code? in our Model Optimization Checklist forum.