Hello Stability Lady,
I don’t have an explanation for the practice you mentioned other than someone having a concern about “validating” the shelf life expiration as the study nears its end. In my experience, commercial product stability study results get a statistical evaluation update at all annual intervals and at or near (as in your case) the final pull point. This would be based more on regulatory “expectation” rather than a requirement. The Q1E guidance lets itself off the hook with the statement: “The recommendations on statistical approaches in this guidance are not intended to imply that use of statistical evaluation is preferred when it can be justified to be unnecessary”, but the language following implies the thought: “but it’s your funeral”. I would visit my internal quality assurance personnel to ask if they have a justification on record for the current policy.
The decision tree is primarily for the initial setting of shelf life or re-test periods, but statistical confirmation practices can also be found in the guidance.