Hello,
Resident Southern staff at East Croydon generally only hold dispatch competency for that location - it is one of the most complex dispatch plans imaginable to remember due to the curves and varying train lengths along with such a high intensity service frequency. Also, some of the East Croydon team actually do agency work for Ontrak and at least some of them have either Purley, Clapham Junction, or Gatwick Airport on their licenses as well - the numbers change from time to time as people come and go, either leaving the role or becoming resident Southern staff.
There are also dispatch staff down the East Grinstead line at Oxted, Hurst Green, and East Grinstead itself, and a small number of relief staff who cover all those locations, but those reliefs do not cover East Croydon and the East Croydon reliefs do not cover the outstations.
It would see a bit of a stretch if they did Victoria or London Bridge also.
Victoria is actually one of the easiest stations possible to dispatch at, pretty much dead straight platforms with one controlled point of passenger entry, so anyone that can do East Croydon could easily in theory do Victoria as well
I hope that helps - may I cheekily ask what inspired the initial question?