History. No count from the nine reviews: the cases were chosen by early additions and do not record the weeks after 2 November. The question comes from S&P's habit of filling a place as soon as a member is bought or split.
Hunch. In ten of the last eleven years S&P named at least one new S&P 500 member outside its review between early November and the end of December.
The outside-the-review market resolves YES if from 2 November to 31 December 2026 S&P Dow Jones Indices announces a new S&P 500 member in place of a company that is bought, split off or removed, and Reuters or the FT confirm it. Changes made as part of the December quarterly rebalance and Okta do not count, but if one release contains both, a replacement for a company that is bought or split off counts here.
We looked for cases where S&P ran its regular quarterly review of the S&P 500 after at least two companies had already joined early in the same quarter. We started in September 2019, the first review S&P announced two weeks ahead. We found nine such reviews from 2019 to 2026, and counted how many companies each review added.