US used to have FO IPs which were just regular line FOs who went into the Training Department. We then had Check Airman doing the checking events (MVs, SPVs, etc). Then APDs who did the type rides.

Now under the New American, the FO IPs are going to be replaced by Sim Ps, which are non-seniority list pilots (mostly retired) who come in and do your training up to your MV (Maneuvers Validation) then the Check Airman take over up to your type ride.

Ground school and Procedures Trainers have always been taught by non-seniority Ground School Instructors or FCTIs (Flight Crew Training Instructors).

The non-seniority instructors do not get a seniority number.