Final Fantasy 14 fans have had quite a lot of requests for Yoshi-P and his team over the years, and besides hats for Viera, the return of PvP Series rewards is one of the most common. It makes sense too, as if you're a newer player, or maybe just got into PvP, it's not nice to be locked out of so many cool armor sets, emotes, minions, and more just because you were late to the party.
Thankfully, it sounds as though players are getting what they want, as the latest live letter digest has confirmed that rewards for past PvP Series will be gradually added to Final Fantasy 14 starting in Patch 7.2. Translation issues caused a bit of confusion surrounding this topic, which was touched upon in the last live letter, but the digest has now just outright confirmed it's starting in the next patch.
Unfortunately, that's all the info we actually have for now, apart from the fact that these rewards can be grabbed via an exchange. We don't know whether it will be via crystals or wolf marks, and we don't know how quickly previous rewards will be made available - or from which series...