The Western workings used lamps,the Southern workings used discs (and obviously lamped after dark etc). No confusion with normal codes - or rather there shouldn't have been, provided Signalmen knew which trains were which and the running order - and anything out of course would be 'boxered' (advised by box-to-box message).
They used lamps then and not discs? Was there not confusion with normal headcodes?
PS Glad you were happy with some examples, in 1960 there were 2 local headcodes off the Western mainlines to the West London Linei (two codes used for four different destinations, hmm), 9 codes on the WLL/Old Oak Common to/from the Southern Central Section, and 5 codes to/from the Southern Eastern Section. Some of these 14 codes were duplicated.