Others will be able to give a more specific date but I believe the new 7.5v light boards were in games either September 2013 or October 2013 and going forward. My ECLE is from Oct 2013 and has the 7.5v boards.
What is the build date on the back of the game? That will help determine if it has the newer light boards. Based on hearing feedback from other early WOZ owners I would think the game would have had a light board problem long ago if it still had the older boards in it.