OK, let me give you a positive story from last year to cheer you up.....
I used to live near a very good, sought-after senior school, but three years ago, somewhat foolishly moved away - not far, but far enough to be well outside the catchment area of previous years. The DCs did not move primary school, as we didn't move far, but DS1 was very glum that all his mates would easily get into the sought-after school, and he wouldn't.
Nevertheless, I put the school at the top of the list, despite the fact that the previous year's catchment stretched only 4km from the school, and we were at least 7.5km away. I prepared DS1 for almost certain disappointment and waited for the 1st March.
Well, he got in, no appeals, straight away offered a place. Another local school was perceived as "improving", which drew more applicants than expected; also many people had made the decision not to bother applying as they wouldn't get a place. I nearly fell off my chair when I heard the news; I couldn't believe it.
So all I can say is, yes, you can use the previous year's admissions as a guideline, but you never know - that school you think of as a long shot may be easier to get into than you think, due to changes elsewhere you haven't thought of. Stay positive!
This year, I am waiting to hear about DD1, who is a year behind her brother; with the sibling rule it should be a done deal, but it doesn't stop me worrying that I've made a mistake on the application etc. etc. and I shall be quite relieved to see it all in black and white on the 1st March. 