Despite an expected record-breaking IPO , SpaceX will still have to follow the rules and wait at least a year before it’s added to the S&P 500, the benchmark behind many Americans’ retirement funds S&P Dow Jones Indices announced Thursday that it is keeping its eligibility rules intact for the S&P 500 and several other major indexes. Indexes are benchmarks that track specific slices of the stock market. The best known is the S&P 500, which tracks 500 of the largest publicly traded companies in the United States. Many index funds and exchange-traded funds (ETFs) hold stocks that mirror these benchmarks in an effort to replicate their performance. These funds are a key part of many 401(k)s, pension funds, and retirement accounts. Earlier this year, S&P Dow Jones Indices said it was considering whether to alter its rules to fast-track companies with massive market capitalizations, the total value of a company’s shares held by investors.…