As far as I can tell, 42 minutes violates United's own minimum connection time for international to domestic at IAD.
Their general MCT for IAD is 45 minutes domestic-domestic or domestic-international, and 90 minutes international-domestic. There are a few connections which allow all the way down to 65 minutes international-domestic, but nothing allowing 42. So if something quoted such a connection at you it would have been invalid per United's published times.
Their general MCT for IAD is 45 minutes domestic-domestic or domestic-international, and 90 minutes international-domestic. There are a few connections which allow all the way down to 65 minutes international-domestic, but nothing allowing 42. So if something quoted such a connection at you it would have been invalid per United's published times.