How to restrict values inserted in hsdl using value set validation

Summary:

We have a requirement to restrict values a user can enter in HSDL template. I have followed this document

Users should not be able to enter position valid grade codes that will be inserted if it is already end dated for a position.

I created a custom value set that pulls grades codes based on the position parameter in spreadsheet row. The value set returns grade codes based on the value set query, and when I input a grade code that does not exist in the LOV, the row is still successfully inserted. This should not be case based on my understanding in the document. Please advise