I, III, V, X2, XI-XIV, Tactics (and its GBA spinoffs).
Also, while there aren't selectable classes in them, characters with effectively fixed jobs also appear in IV, VI, and IX; they may not be called "White Mage" or "Black Mage" in every game, but (for example) Porom and Palom are precisely that, and the game references job names (e.g. Tellah is a Sage, Edward is an infamously "spoony Bard," Kain is a Dragoon, etc.) Vivi, for example, isn't called a BLM, but absolutely 100% is one.
So, by my count, that's ten true mainline games (assuming you don't count X2 as a mainline game) out of a total of sixteen, and two further prominent, well-known games of the series (one of which has even further spinoffs).
I think it is fair to say that, while FF does do its own thing with each new game, the pattern generally holds. FFII, VII, VIII, and X are exceptions, and worthy of note as a result, but still exceptional.