Not sure when four-car service started on the North London Line, but
spotted two 378/2 units on Tuesday this week. One was 378210 which I
presume had a fourth car added after a year or so as a three-car, and
378226 which was built as four-car from new.
http://commons.wikimedia.org/w/index..._Centra l.JPG
http://commons.wikimedia.org/w/index..._Stratford.JPG