The quark model was originally just a very good classification scheme to organize the large number of hadrons that were being discovered starting in the 1950s and continuing through the 1960s but it received experimental verification beginning in the late 1960s and continuing to the present.
The quark model was originally just a very good classification scheme to organize the large number of hadrons. These hadrons were being discovered starting in the 1950s. These hadrons were continuing through the 1960s. It received experimental verification. It was beginning in the late 1960s. It was continuing to the present.