PO DFF Captured Value which is not part of manage values

Summary:
Hi Team
We have one strange issue
We have one DFF in PR and same DFF in PO
For PR we are using A as Value Set and for PO we are using B as Value Set
For A value set we have 1,2,3 as values
For B value set we have 1,2 as values
It means our expectation is whenever we have PR with 3 as value - in PO DFF should be blank
But for some PO we are seeing value 3 in PO Dff
PO DFF valueset dont have 3 value
How can it capture?
Anythoughts will be helpful
Thanks

Content (please ensure you mask any confidential information):