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How does an index rearrange its major holdings
S & P Index Announcements would have notes on when there are changes to the index.  For example in the S & P Small-cap 600 there is a change that takes affect on Feb. 19, 2013. As for how index funds handle changes to the fund, this depends a bit on the nature of the fund as open-end mutual funds would be different than exchange-traded funds.  The open-end fund would have to sell and purchase to keep tracking the index which can be interesting to see how well this is handled to keep the transaction costs down while the ETFs will just unload the shares in the redemption units of the stock leaving the index while taking in new shares with creation units of the newly added stock to the index.