Many of the 3 class 777s do not yet have Economy Plus seating, so don't get too excited yet.

I think I sat in row 18 on EZE-MIA and it sure wasn't E+!

Also, the crew rest seats on the non E+ planes are in a different location (I think in the back of the forward coach cabin, not the front), so the lack of E+ may explain why you are getting a crew seat assigned if the flight is international.