I asked my wife (audit, big 4, alternative investments) why there would be an amendment to an S1 and while she doesn’t deal with companies going public directly, she said that amendments are pretty common for funds that go public. The reason being is that a company can file for S1 (or Form 10) before the initial seed audit is complete and SEC or audit firm may have some additional requirements/disclosures to be added.

Perhaps someone for Finance world can chime in with additional info.