<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Empress:
What you planned to do is perfectly legal. It's called end-on-end ticketing meaning you're combining 2 tickets to get to your destination.
In the fare rules for both DFW-NRT and NRT-SIN, you'll see:
Code:
END-ON-END - -PERMITTED
.... </font>
In my experience, a travel agent (and maybe even UA) will put this kind of construction on a single ticket, even. Even if they don't, I've checked in for this sort of thing and had no problem checking bags through, getting all boarding passes up front, etc.
I even would try to get assistance in case of irregular ops as I bet that has been known to happen before (although I haven't run into this problem yet myself, fortunately).