This thread from late 2009 estimated the number of "complete" T206 sets at around 1k.
http://www.net54baseball.com/showthr...ight=t206+sets
I doubt that 1 in every 3 pre-war collector has a complete T206 set. I think the number of collectors is higher and the 20k number wouldn't surprise me a bit. I also think the number of "complete" T206 sets is lower but that's for another thread.