A bit confused here...

I had a couple of trans-Atlantic flights in J, and right until departure I could see on expertflyer how the seat next to mine was blocked with an "X". When I changed seats on lh.com, the "X" on expertflyer moved with me. That led me to conclude that they do seat blocking for status pax also on longhaul flights in J.

Now I have two flights to the Middle East in J. There, no "X" next to my seat. So no seat blocking?

Or does this have to do with aircraft type? US flights were on B747-8, MidEast is on A333.

Thanks.