I have supplied for 3+ years, as a DECE. Advancement is hard.
I have applied to many jobs. Received one interview. There is a A, B , C list and it is quite hard to get onto the B.
I have worked in one school for longer than 4 months (which if hired as an LTO for 4 months min, you can be put into the LTO hire list- aka the B list) but I was considered an occasional supply the whole time while the school waited to have to post a position and hire from the A and B lists.
Where this was a favour to me to keep me in the position, I ended up being bumped out after Christmas.
Loved the time I spent, and gained much experience and contacts throughout the year.