I connected on separate tickets via NRT twice this week without any problems. Outbound JAL First to Thai First (1h50 connection) was the easiest as there was no security and I was escorted by a JL rep all the way from my inbound plane to Bus Shuttle Gate. 70. Today's return Thai First to JAL First (2h30m connection) was not as pleasant as there was no escort and I had to clear international connection security with hundreds of others. I just had carry-on bags which made it doable.