But Star Trek Online and Countdown are not one and the same. Treklit and STO could both include Countdown in their post-Nemesis continuities, while getting there in different ways and then taking different directions afterwards.
Data's exact words from Countdown
are that "my neural nets were successfully imprinted onto B-4's existing programming." That reference was no doubt the basis for the STO version, which elaborated on it. And there's no way to reconcile that statement with TPoM, in which only Data's memories, not his neural net, were downloaded into B-4, and it was a failed imprint that almost killed B-4.