Bonds have default risk categories like AAA, BBB, etc. Bond funds often choose bonds based on these categories.
With ETFs and Mutual funds, there is a level of survivorship bias because the fund is ranked based on historic returns.
Does a similar historical survivorship bias exist in ranking bond funds? For example, if a company/nation is upgraded to A from B, then will the bonds that used to have a B rating all be upgraded, their price jump up, etc thus making certain bond ETFs return look artificially high?