I don't think any specific number defines a premade. w41 had a premade of 3 players that never recruited anyone else. If they had joined and recruited more people than they started with right away, I wouldn't refer to it as a premade.
EDIT: These are all the tribe changes they had, and look at the dates:
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nateyboy04 Left 18th December 2009 - 22:00 642,830
poopPLUSlog Left 18th December 2009 - 19:00 782,748
dwilkes Left 17th December 2009 - 07:00 1,456,196
Stalker1988 Joined 09th December 2009 - 01:00 1,118,467
nateyboy04 Joined 30th November 2009 - 22:00 611,576
poopPLUSlog Joined 30th November 2009 - 16:00 630,946
dwilkes Joined 29th November 2009 - 22:00 1,212,522
raptorfree Left 29th October 2009 - 16:00 0
Living-Legend Left 05th October 2009 - 19:00 0
Incoming Spears Left 04th August 2009 - 13:00 0
crisco Joined 11th July 2009 - 10:00 62
Living-Legend Joined 11th July 2009 - 01:00 51
raptorfree Joined 11th July 2009 - 01:00 60
Incoming Spears Joined 10th July 2009 - 04:00 52
Me love you long time Joined 10th July 2009 - 01:00 26
Mo Points Mo Problems Joined 10th July 2009 - 01:00 32
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6 players joined, 3 made it past 1 village. 5 months without recruitment. That's a premade, even though they only had 3 players.