Concatenate expression for initial value for key column.

[Atlas]

I don't know whether it is just behaving normally. But I don't get the result I want. I have a concatenate expression for a key column, which creates a unique ID from the combination of two precedent values from the dependent dropdowns list from the GR_Code and CT_Code

GR_Code values come normal. But for the CT_Code part, it brings the first value from the dependent values of GR_Codes.

CONCATENATE(GR_code],".",[CT_code],".",UNIQUEID())

Thank you for your time.