MJ has it spot on.
There was a duty FI sitting in ops who would authorise each solo flight and pop a little sticker into your log book to that effect after checking your map and individual wind limitations (which were set by your own instructor).
If you didn't already hold a PPL before you started (an unnecessary additional cost as far as I was personally concerned) then you won't get an SEP out of OAA (or any integrated course I suspect?). If you did already hold one, then you may have been able to negotiate with your examiner to sign off a renewal during a normal check ride - alternatively you could cough up for a separate renewal flight with an examiner.