"Basil Jet" wrote

You must be the only living boy who hasn't been to New Cross. Allegedly,
the platform numbers are to distinguish from New Cross gate, although they
aren't really near enough to warrant that.

Until the Grouping both stations were named New Cross, and were only
distinguished as New Cross (Brighton Line) and New Cross (South Eastern
Line). Into the 1940s there were porters on the East London Line who
announced trains as for New Cross Brighton Line. The locomotive depot next
to New Cross Gate station was known as New Cross shed until its closure in
1947.

Peter