Its good to play conservative, especially when something like this happened to both hives and you have no other options.
However, I dont think the LW issue is as simple as open brood. For example, hives requeen themselves and spend atleast 2 to 3 weeks without any open brood at all while they wait for the new queen. But then again, I just witnessed a small swarm that has no queen (I looked everywhere) that went LW within a week in their new box.
Good luck.
