No, we do not, and no, neither did they think they had 'it'.<quoted text>
All these guys thought they had it right...
1676 Olaus Roemer
1726 James Bradley
1849 Armand Fizeau
1862 Leon Foucault
1879 Albert Michelson
1907 Rosa, Dorsay
1926 Albert Michelson
1947 Essen, Gorden-Smith
1958 K. D. Froome
1973 Evanson et al
1983 Adopted Value 299,792.458
So we just all now "know" we've got it right this time, yes?
Because, of course, all those other guys "knew" that had it right, too.
Newton brougt out his theory of gravity. Many years later, Einstein was able to improve on it with his theory of Relativity.
A theory is an explanation of facts. Each generation, as technology improve, we obtain more bits of data, which are more accurate. This allows us to improve, ammend or change set theory. Newton's Law of Gravity is still being used, even by NASA for near earth applications, because it is simpler and easier to apply.
It's like cars. We can make smaller engines give more horsepower. Modern mass production cars are faster than sports cars twenty years ago. That does not mean the classic cars like the Jaguar E-Type, the Ferrari F40 and the Aston Martin DB5 are crap.