ΔE 21.5, loose: different enough that you should pick on purpose. Old Rose is a little lighter, cooler than Flat Earth.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Old Rose is a little lighter, cooler than Flat Earth.
The same difference applies the other way round: Flat Earth 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 Flat Earth on the colour wheel See Old Rose on the colour wheel
All matches: Flat Earth equivalents · Old Rose equivalents