ΔE 8.6, close: similar, with a visible difference side by side. IJA Olive Green is a little lighter, cooler than Overlord Olive.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). IJA Olive Green is a little lighter, cooler than Overlord Olive.
The same difference applies the other way round: Overlord Olive is a little darker, warmer.
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 Overlord Olive on the colour wheel See IJA Olive Green on the colour wheel
All matches: Overlord Olive equivalents · IJA Olive Green equivalents