Do the individual pieces of LEGEND Pokemon count toward the 6 Pokemon needed for a player to declare themselves a winner when "Lost World" is in play?
Yes, each LEGEND Pokemon card counts as one Pokemon toward the requirement.
Source: Call of Legends FAQ (2011-02-10), PUI Rules Team (2011-02-10)

Relevant cards

Note: All applicable cards may not be listed below.
COL1_81