If I only have vanilla SWTOR, I can still access level 50 vendors, all the flashpoints up to that level, all the gear up to that level. Everything I got with my vanilla copy of the game. If I buy Rise of the Hutt Cartel, I can access all of the ROTHC content, equip all the gear, access all the content. If I have both of those and chose not to or was unable to afford Shadow of Revan, they do not suddenly lock a bunch of the ROTHC content behind SOR, requiring me to advance to a certain quest point in it in order to do things like gain Makeb reputation again. I do not suddenly find that all the gear vendors have had everything replaced with gear flagged with "Requires Shadow of Revan"