If your seat does not have an FAA label (mine does not have an obvious label), you can print the info from the manufacturer's web site.

Also, I found that our infant car seats (Combi) did not belt into the seat unless I used a lap belt extender. In retrospect, I think a mistake I made was to use the snap-in base rather than just using the seat, but since I was a new parent I didn't fully understand the 50 pages of directions that come with the seats.

Finally, not necessarily for the OP, but a benefit of the international 767's and 777's is that there is a bassinet connection in the bulkhead that can be assembled. Seatguru implies that it's not available domestically and unless you make a reservation. Maybe I just got lucky on my SEA-IAD flight and it was available.