Some will be people from Bham who have shared their scores in order to be given a rank.
Others will be those living in Worcs, Solihull, Coventry, Leic etc who, although not in the priority area, live close enough to make the GS a possibility if their DC score highly enough.
all right. So we are not told how many of them then?
All we can do is work out the number, ~1000, as you have done. How many of those are seriously considering applying for a Warks GS, we have no idea ...