Someone posted a couple of questions about s.47 but they seem to have disappeared, but to answer:
The Hospital Managers must refer after 3 years as per section 68 (see Schedule 1, Part 1, Para 10).
First renewal must occur 6 months from the date of the order (see Schedule 1, Part 1, Para 6).
As for ‘Notional 37’; it’s is a made up term, usually applied to when a s.47/49 reaches release date and the 49 falls away, whereupon the person is treated as though they were detained under s.37 from that date. When an unrestriced s.47 reaches release date, there is no effect because the person is already being treated as though they were subject to s.37.