A backtest is a record, not a forecast. Each of these answers one question over one
stretch of months, and several of them would answer it differently over a different stretch.
Where that matters, the page says so.
Nobody earned these returns. They are index returns with no fund fee, no spread and no
tax taken out, and they assume a rebalance every year that nobody forgot.
These are generated from the same monthly data the
backtest runs
on, and rebuilt when that data is. To run a mix of your own instead of one of these, the
backtest takes any weights you like.