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DaveThe best discussion of T206 backs is in Lew Lipsett's Encyclopedia of Baseball Cards, Volume 3. His discussion takes numerous pages with pictures of the backs, along with tables of what cards are available with what backs. A few tidbits: there are 16 different backs, and some were in the three series you mentioned, called the 150, 350, and 460. Other backs didn't have the series. There are 156 cards in the 150 series in 1909, 327 added in 1910 for the 350, and 40 more added in 1911 in the 460 series. There are 389 players in 523 different cards.
This reference is available in reprint as part of a combined set of volumes 1, 2, and 3, which is readily available and highly recommended for any vintage collector. An ebay search for "Lipset baseball" returned several BIN listings at $29.95, all from the same seller. Here's a link:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=641&item=5181461939&rd=1&ssPageName=WDVW