Sailfish X is just the pay-for-features scheme for official ports.
Arguably it started as, or still is, Sailfish OS for officially supported devices not made by Jolla (basically Xperias and the Gemini). There didn’t use to be a free trial then, so it just meant “official Sailfish for other devices”.
Everything on that list was either made by Jolla, is available in the Sailfish X programme, or was available through it.
Jolla != Volla.