You need to rebalance if the stocks included in your top 5 index change, i.e. if some new stock displaces one of your original 5. Otherwise you've got a fund of

You need to rebalance if the stocks included in your top 5 index change, i.e. if some new stock displaces one of your original 5. Otherwise you've got a fund of 5 stocks chosen by some metric on historical date blah -- which may be a reasonable idea but doesn't seem to align with the spirit of "S&P 5".