ΔE 17.7, loose: different enough that you should pick on purpose. Tarnished Steel is noticeably darker than Shining Silver.
Can I use Tarnished Steel instead of Shining Silver?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Tarnished Steel is noticeably darker than Shining Silver.
Can I use Shining Silver instead of Tarnished Steel?
The same difference applies the other way round: Shining Silver is noticeably lighter.
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.