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something that might affect someone’s opinion of whether to invest or not, so IT IS A MATERIAL EVENT.

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Actually material events are events that may have an impact on the share price. The link below is a list of what the SEC considers mandatory disclosures. Any other disclosures are up to the company.

After the fact the SEC can but is not required to make a determination on whether a non-mandatory disclosure should have been made. They take into consideration if that information would have a substantial impact on the share price. Since that determination is subjective and they have a limited budget they usually restrict it to that which would have a negative impact.

https://www.sec.gov/fast-answers/answersform8k