I collect old Pears Cyclopaedias. I'm just pulling a few editions of the shelf as we speak. The 1898 edition shows the county town of Sussex as Chicester, as does the 1927 edition. .... okay the county town is shown as Chichester up until 1935/1936  the next edition I have is 1939 and the county town is shown as Lewes. I don't have any further details.