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Got it in Silver by buying Red, Gold and another Gold with Celebi.
Almost got in Diamond by buying Emerald and FireRed, plus local trades, but I missed 30 or so, like Kingdra. Eventually used Action Replay, since it was impossible to get some, like Mythicals anyway.
Needing to use a second DS to transfer to Black started to dwindle my interest, but with GTS, Dream Radar and Black 2 I got all new ones except Victini, but at that point I couldn't be hassled to transfer them individually.
Got all new ones in Y, but only to "complete" my Pokédex 3D Pro.
The enjoyment I had by scrolling through the whole dex in Silver and Diamond was then gone with the removal of the NatDex in S/M.