Re: Mating nucs
Like you I am still experimenting on my version of queen grafting. I still not know what I am doing to help increase the chance of a mated queen coming back. For sure, your virgins got balled within minutes of introduction. If not sure then do an experiment to see. Five minutes is all you need to see this process in play. I did! No, they did not cross compartment and got kill either.
So far the success is with spacing the mating nuc farther apart like 5 feet or so in a row facing south. I use individual mating nucs. Four out of four came back so far. But my number is small to compare. Surely the virgins are confused coming back when all the hives looked the same. When she entered a wrong hive then the workers will kill her. Introducing virgin into existing established nuc will not work as they got balled most of the time from my experience. I had lost so many mated and virgins this way. So the only solution I can think of is to cage the qc at almost hatching time to put inside the nuc. They will chewed out the qc if not protected. With 200 qcs you will need many qc cages for that. This is another investment I am sure you will consider.
Also, caging a virgin inside nuc hive will not work as I had tried that already. I believe a virgin should be able to crawl all over the hive to feed herself and develop her presense in the hive before taking her mating flight after the 7th day. The bees are more acceptale to her this way. If I take a virgin into another nuc she is dead by balling. Same thing with a virgin coming back from her mating flight into a nearby nuc instead of hers.
So try to space out the nucs farther apart and caged the qc before emerging. I had tried masking her scent but that did not work either on introduction. Look like you have a problem that the virgins got confused on their way back to the nuc hive after their mating flight. Don't try the shot gun approach that waste your time and energy. You need to figure out a sure way timing it down improvement process.
Don't mix foreign bees into a virgin hive. She might get balled 100% of the time! When will you ever learn, huh?