Not an error… there’s a cost element to providing TIGER feeds for more stations.
I am surprised that a state owned railway company as large as Southeastern can not afford that. At neighbouring GTR they have 100% of stations on Tiger despite having double the amount of stations. It is probably just someone at Southeastern management trying to cut costs by limiting Tiger to only a few stations.
I will say that Southeastern seems to spend a lot less money on their CIS compared to other TOCs. For example Southeastern still have 45 smaller stations (eg, Crowhurst, Folkestone West, Martin Mill, Stonegate, etc) that use basic Text To Speech (Acapela Rachel) announcements from the Infotec boards rather than proper Anne and Rob announcements. Meanwhile at neighbouring GTR they have proper Anne and Matt announcements at 100% of stations. Even tiny little Doleham has Anne announcements now.
It would be good if the ongoing nationalisation of all our TOCs brings some standardisation and brings all TOCs up to the same level. Hopefully all stations will be on Tiger then. Or maybe even a new replacement for Tiger will be developed by then.