I had a quick walk around the Brighton and Preston Cemetery. It is clearly signposted and has its own entrance gate, so you wouldn't mix it up with any other cemetery. It is the Extra-Mural and Woodvale cemeteries that I am mixing up, as on the ground they seem to run into each other and don't have clear boundary lines, but thanks for that advice on how to read the PDF map.
The Brighton and Preston Cemetery, the bit I saw of it as it is huge and would probably take ages to walk round it completely, seems to be much more recent graves than the Extra Mural or Woodvale. The oldest ones seemed generally to be people who died in the early twentieth century with a very rare one or two who died at the very end of the nineteenth century.