This requires an analysis of the risk of the withdrawal procedure failing and the potential severity based on possible hazards. In my risk assessment I would also consider how many product withdrawals there have been historically, how effective the withdrawal was and the results of any previous mock wothdrawals.
Here is guidance given by IFS:
IFS Food Version 6 Guideline - Typical auditor questions, examples for KO/Major and cross references for IFS requirements
5.9.4 The feasibility, effectiveness and timeliness of implementation of the withdrawal procedure shall be subject to regular internal testing, based on hazard analysis and assessment of associated risks but carried out at least once a year. This shall be carried out in a manner to ensure the effective implementation and operation of the procedure.
What do you have to check? What must be asked?
How is effectiveness of withdrawal tested?
How often is effectiveness of withdrawal tested?
<withdrawal test results>
KO / Major
When withdrawal procedures are not tested or when test results have shown that the procedures are ineffective but no corrective actions were implemented.
Cross reference - IFS requirements, important european directives, other comments, US american legislation