Hey there! They are not required for the seal, but they come from regular Gambit. Because Gambit and Gambit Prime are being infused into one game mode, that is why they are being vaulted. It may still be called Gambit Prime, or it may have a new name. This is most likely the reason.
[quote]Frontier Sage is a requirement for Dredgen, a title confirmed to stay after the DCV in season 12.[/quote] Pardon my ignorance, but where are you getting this info from? It is not one of the listed triumphs in the seal.