It is worth looking up the published account for your relevant school on the Charity commission website. You have to dig a bit but they're all on there in pdf form.
As bursaries are one of the things the Charity Commission looks at carefully, the schools tend to list a fair bit of information about them, and you should have a fair indication as to what happens.
In my experience, since the CC first started examining bursary pots carefully, bursaries have been reallocated where possible rather than rolled into subsequent years. That said, I doubt that they will be given to those who accept a full fees place, as you're essentially signing to say that you can afford it, but instead it will go to those who contact the school, make their plea, and wait.
I'm a bit confused as I've made a plea for a bursary but the deadline for acceptances is soon. How can they re allocate until after the deadline as don't the schools need to see who has accepted and who has decline the bursary offers.
If I accept a full fee place I realise this will show I can afford a place but if I don't I lose my daughter's place! The bursars said they won't know till after the deadline? What should I do?