The questionable claim
A churn predictor includes account_closed_date while predicting churn before closure.
Investigate
Identify the unit of analysis, denominator, population or information boundary. What extra evidence would be needed? Write a corrected statement first.
Diagnosis and repair
The feature is not available at prediction time and leaks the outcome. Define the decision timestamp, remove unavailable information, split by appropriate time/entity and compare against a simple baseline.
Prevention
Add a test or review question that catches the error before publication. Save the original and corrected explanation so your reasoning is auditable.
Try the activity before reading its reference. Keep your sources, commands and assumptions with your work. Companion activities are unsaved self-practice and do not award a certificate or change lesson progress.