A CSA-box “will they skip this week?” model still sees the same signup fields, but after a new pickup rule the old “loyal” pattern now predicts the wrong skip. What should the tester name that change?

Signup fields stay the same, but after a new pickup rule the old “loyal” pattern now predicts the wrong skip. That is concept drift: the relationship between inputs and the correct output has changed. It is not merely a new input mix, not overfitting, and not a Chapter 5 uniqueness gap.