There's an exception to every rule. (Perhaps even this one?) I peopled my OB hive from a failing hive that wintered over. I assumed a poor queen and wanted her for my hive because she wouldn't swarm. There are 2 palm sized patches of brood on each side one frame of a 3 frame hive. The other day I noticed that there were 2 queens in it. They may be related but one is black and the other is yellow. I would have seen a queen cell. At first they were on opposite side of the comb.
"If I watch long enough I may see them fight", I thought. Then I saw them both on the same side. As they drew closer, I got ready for the match. They just walked by each other. They both lay. In fact I saw one laying while the other stood by her head. Have seen them just hanging out together.