Went through IOT in 91. PQOs was called SERE then (Specialist Entrant & Re-Entrant I think?), or Tarts and Vicars if we were being unkind (if somewhat accurate).Not entirely true, I'll explain why.
Seniority on graduation is determined by a number of factors; educational qualifications (eg if you have a Bachelors / Masters degree), prior service in the University Air Squadron system or service in the ranks, and (for PQO's) professional qualifications / accreditation. The military status of any officer cadet, untill commissioning, equates to that of an Aircraftman (i.e. a Private).
For the purposes of graduation ceremonies, the cadet's uniform is prepared with their prospective commissioning rank, as in the case of the rather attractive Flt Lt (desig) in the photo concerned. Upon reaching graduating standard, cadets then spend about a week doing admin / parade prep (colloquially known as 'drink-and-drill') before marching off the square (nowhere near as impressive as a Sandhurst graduation, to be fair) and then head off to Phase 2 training. In the RAF system, that's where the 'thinning out' takes place; flying training will bin about a half of all prospective pilots / navigators, with some re-branching to ground streams, some leaving the Service, and some transferring to the green / dark blue.
When I was a RAFC cadet in the early 90s it wasn't unusual to see PQOs march off the parade square as a Wg Cdr or a Gp Capt (principally Medics with niche qualifications).