This POV comes from Kuhn;
I'm applying it to math.
Modern formulations of mathematical theories are not their orginial
formulations: they are the theory \emph{as refined} by succeeding generations.
Still recognizably the same theory, but in a more polished
and better-understood form.
Some examples:
Calculus
Similarly, calculus today is not Newton and Leibniz's;
it is as refined, especially by Weierstra\ss.
Riemannian geometry
Riemannian geometry today is not the theory as developed by Riemann:
it is the theory as refined
(Kuhn's example)
Newtonian physics is not Newton's physics:
it's that theory as refined, particular in the Lagrangian and Hamiltonian
formulations.