The traditional rollback mechanism deployed in optimistic simulation is state-saving. More recently, the method of reverse computation has been proposed to reduce the amount of memory consumed by state-saving. This method computes the reverse code for the model during rollback execution, rather than recalling saved state memory. In practice, this method has been shown to offer memory-efficiency without sacrificing computational efficiency. In order to support reverse codes in the model, events must continue to be preserved in the system until fossil collection can be performed. In this paper we define a new algorithm to support perfectly reversible model computation that does not depend on storing the full processed event history. This approach improves memory consumption, further supporting large-scale simulation.