I believe PREMIUM means that you are eligible for seat pre-selection in the "Premium Seating" area (usually rows 5-7). You get it if you are Elite or on a Y fare (and sometimes if you change your flight and the agent gives you a new record rather than spend the time to go in and modify your existing one).

FQTV means nothing in particular. As noted, it appears if you are on the first leg of a connecting itinerary and are claiming WP miles.

VLTR means volunteer for reaccomodation. It is usually accompanied by two numbers (eg. 1/4) so that a gate agent can quickly track the number in your party volunteering and your priority number for bumping.

CORP and EBPK are for travellers using corporate accounts or E-Biz Perks accounts to book their flight.