ΔE 16.9, loose: different enough that you should pick on purpose. Old Gold is a little darker, warmer than Grave Robber.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Old Gold is a little darker, warmer than Grave Robber.
The same difference applies the other way round: Grave Robber is a little lighter, cooler.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Grave Robber on the colour wheel See Old Gold on the colour wheel
All matches: Grave Robber equivalents · Old Gold equivalents