There have been multiple iterations of the “metric system” since it’s introduction in 1792–1795, most notably the original 1795 draft variant, then the CGS (Centimeter-Gram-Second) version, then the MKS (meter-kilogram-second) variant, with the most recent incarnation being the International System of Units (SI).
That’s why there are plenty of metric units, but not all of them are SI units. :)
Edit: Changed “1892–1895” to “1792–1795”. Lol, whoops.