Clearly I must have made a mistake, the S&P500 did not gain 150% in 2016. So what did I do wrong, or is the data in FinancialData in error???

From the internet -- gains of the S&P500 by year

Table constructed from Mathematica

My code

rus3RtnYr = FinancialData["IWV", "Return", {{2010}, {2021}, "Year"}];
rus2RtnYr = FinancialData["IWN", "Return", {{2010}, {2021}, "Year"}];
spxRtnYr = FinancialData["SPX", "Return", {{2010}, {2021}, "Year"}];
djRtnYr = FinancialData["^DJI", "Return", {{2010}, {2021}, "Year"}];

Grid[Prepend[
  Transpose[{Map[
     DateString[DateList[#], {"MonthName", " ", "Year"}] &, 
     Flatten[rus3RtnYr[[2, 2]]]], 
    Map[PaddedForm[#, {2, 1}] &, Flatten[rus3RtnYr[[2, 1]]]], 
    Map[PaddedForm[#, {2, 1}] &, Flatten[rus2RtnYr[[2, 1]]]], 
    Map[PaddedForm[#, {2, 1}] &, Flatten[spxRtnYr[[2, 1]]]], 
    Map[PaddedForm[#, {2, 1}] &, Flatten[djRtnYr[[2, 1]]]]}], {"Date",
    "Russell 3000", "Russell 2000", "S&P500", "DJIA"}], 
 Background -> {None, {LightRed[.3], {White, 
     Lighter[Blend[{Blue, Green}], .8]}}}, 
 Dividers -> {{Darker[Gray, .6], {Lighter[Gray, .5]}, 
    Darker[Gray, .6]}, {Darker[Gray, .6], Darker[Gray, .6], {False}, 
    Darker[Gray, .6]}}, Alignment -> {{Center, Center, Center}}, 
 ItemSize -> {{9, 8, 8, 8, 8}}, Frame -> Darker[Gray, .6], 
 ItemStyle -> 14, Spacings -> {.3, .8}]