Vlookup will look up exact matches for capital letters and lower or
proper case.

There may be other characters (like spaces) in one of the cell
entries, which will return no match. Examine 1 or 2 that should match
but don't, and you might find the issue. For example Bob Smith will
look up BOB SMITH. But Bob Smith will not lookup Bob Smith. Spaces
can be leading or trailing in the cell. Check that out.

And make sure you use the false switch (i.e. vlookup(A1,mytable,
2,false).