Actually, ignore this - I found the issue. (My meddling, not yours - my apologies)
Ended up because I removed the no show (due to other reasons) by remming the line define('MDL_F2F_STATUS_NO_SHOW', 80);
it inadvertantly caused an issue further down, where it would not ever show the person as having been booked in to attend the session.
Cheers
Peter