I think it's more common than people think, because you stop looking for queens when you find the first one. I've never had 3 queens that I know of. I've had double queens 3 times that I know of and I've only got a dozen hives. My case, like yours, found and pulled the marked queen, the went on to rob a couple of frames and found a second. Then last month I pulled my favorite queen to get queen cells, put her in a nuc, went back ten days later to collect the cells.... No cells! Sure enough, after a frame by frame inspection, found a second, laying queen.I have been using a 10 frame single deep started in March from a package to split to nucs or use frames of brood from this to bolster other hives. It has always had an enormous amount of brood in it and have always thought wow this is a really nice productive queen.
I went in to today to rob a couple of frames of brood for a weaker hive and a nuc. The second frame I pull out and inspect there is an unmarked queen so I think odd there was a marked queen in there last week, and go ahead an mark her. Next frame I pull out there is another unmarked queen so I mark her too. Now I am interested so continue inspecting and sure enough there is my original marked queen
How common is it to have multiple queens living in harmony in a single deep hive. I have never seen a queen cell in this hive so I am a little confused as to how these other two queens got there in the first place. No wonder there was so much brood in there.
Cool stuff! Of course you have to wonder how great the queen is now. Like me, my favorite queen, was really 2 queens!