Precisely. This isn't the same Data that we saw from "Encounter at Farpoint" through to Nemesis. As Altan Soong himself said, this being contains "an awful lot of Data", but it's not the same individual – even if he has the same memories. It's a new consciousness, combining parts of Data, Lore, B4, Altan Soong, Lal... it's much more than just the straight "reincarnation" Picard had. It's more like a Trill symbiont being transplanted into a new host. It's a new Data. I'm wondering if by the end of the season he might change his name to reflect his new existence, becoming "Soong" or something.
While I understand the point you're making, I do think you're incorrect.
This *is* the same Data that we were with from Encounter at Farpoint all the way up to when Data turned B4 off in Nemesis. This is the manifestation of Data from that time, plus Lore, plus B4, Alton Soong and Lal.
In simple terms..think of Data as a ship. Along the way that ship is amended with parts from a sister ship, some custom modifications, etc..
It is still the same ship, just *more* than it was before.