Yep, looks like it’s the index column thing that’s getting you. For vlookup the first column has to be the one that will continue the value you are looking for. So if you move the BMI column into column A you’ll be good.
Nope, I just tried two ways of altering the spreadsheet so the data so it would be in Column A. First I moved the information to Column A and I also copied the information to column A and it is still throwing the #N/A error. I did alter the formulas to look for the data in column A.
When you use vlookup to search an array of cells for the data, the very first column the vlookup looks at in that array has to have the value you are looking for. So if you leave the BMI data in column G, the date has to be to the right of it. A simple option is to just have the cells in H setup to direct reference the data in column A (ie. cell H9 =A9; cell H10=A10 and so on), then just hide the column.