Understanding the many-body dynamics of isolated quantum systems is one of the central challenges in modern physics. To this end, the direct experimental realization of strongly correlated quantum systems allows one to gain insights into the emergence of complex phenomena. Such insights enable the development of theoretical tools that broaden our understanding. In our study, we theoretically modeled and experimentally probed with Ramsey spectroscopy the quantum dynamics of disordered, dipolar-interacting, ultracold molecules in a partially filled optical lattice. We reported the capability to control the dipolar interaction strength, and we demonstrated that the many-body dynamics extended well beyond a nearest-neighbor or mean-field picture, and could not be quantitatively described through use of previously available theoretical tools. We developed a novel cluster expansion technique and demonstrated that our theoretical method accurately captured the measured dependence of the spin dynamics on molecule number and on the dipolar interaction strength. In the spirit of quantum simulation, that agreement simultaneously benchmarked the new theoretical method and verified our microscopic understanding of the experiment. Our findings paved the way for numerous applications in quantum information science, metrology, and condensed matter