The approved petition and its supporting evidence, dated share registers for both entities, the organisation chart as filed, and payroll for the receiving company. Those become the baseline against which any later reorganisation, promotion or relocation is measured, and reconstructing them years later is expensive.
Keep the baseline, because change is measured against it
Companies file a petition, receive an approval and put the file away, which is exactly the wrong instinct in a classification whose validity depends on facts continuing to be true. Four things should be retained in an accessible form. The approved petition with its exhibits, because that is the description of the arrangement that was authorised.
Share registers for both entities as at the filing date, so that any later change is visible as a change. The organisation chart as filed, which is the thing a promotion or a redundancy round quietly invalidates. And ongoing payroll and financial records for the receiving company, which demonstrate that it is still doing business.
When a transaction closes or a restructuring is announced, the review is then a comparison rather than an investigation. The same records support the extension, and an extension prepared from contemporaneous documents is materially stronger than one assembled from memory in the final month.