In the conventional thermal leptogenesis framework within the type-I seesaw model, it is generally assumed that only the CP-violating decays of the lightest right-handed neutrino (RHN), \(N_1\) , contribute to the final \(B-L\) asymmetry, while any asymmetry generated by heavier RHNs ( \(N_2\) and \(N_3\) ) is erased by \(N_1\) -mediated washout processes. We revisit this assumption by analyzing decays, inverse decays, and scatterings. Our findings show that this assumption holds only if all RHNs are in the strong washout regime. If \(N_1\) is in weak washout, the impact of \(N_2\) and \(N_3\) can be minimal depending on their washout parameters. Conversely, if \(N_2\) or \(N_3\) is in weak washout, their contribution to the final asymmetry can be significant even with \(N_1\) in strong washout, a phenomenon we term the “memory effect”. We identify the parameter space where this effect becomes relevant.