Say I'm comparing different models of a particular car. There are four models in total, each released a year apart. The current model would be the newest one, and the "prior" model would be the one before the newest one.
Is there an equivalent adjective that describes the model before the prior one? I could call it the "second-generation" model, but then that's no longer relative to whatever generation the current model is (unlike "prior," which always means "the one before the current one").