I believe it's down to Southern still providing the data on the boards and station announcements for the ELL stations south of New Cross Gate on behalf of LOROL, this is a legacy from the Southern franchise. These were supposed to have changed over, but kept as part of cuts to the refurbishment programme.

What LOROL can do is request Southern as the contract provider is ask them to abbreviate the word Islington to bring back the 2nd and 3rd trains back on the departure board.

LOROL provide their own service and departure boards for stations between Surrey Quays and Highbury and Islington.