Yup, every year since 2012* I take the UK membership stats found on page 46/54 of the annual report pdf and put them in a google spreadsheet, probably takes no more than a couple of hours, and that could probably be streamlined if I was keen as the layout requires a fair bit of formulae tweaking. Usually something interesting to be pulled out of the stats. When I did the 2019 numbers I posted it to the UK equivalent of here, and it triggered 6 pages of replies, some of which may even have been related to the membership stats in the spreadsheet.
* and it goes back to the late 90s thanks to someone else starting the thing, I just took over and moved it to a google sheet. Standing on the shoulders of giants, as ever.
Unless the rules have changed since 17 years ago (and I can't believe they would have changed to be less restrictive), unless your son was a Tiger, there is no requirement that a parent must stay with a Scout on an overnight trip.
First question would be, is the person who signed all 9 cards a registered MBC for each of the MBs? It is amazing at times how many registered adults do not understand that just because they are an ASM or a SM, they are not automatically authorized to sign off on what ever MB they choose.
You weren't in violation of any rules. From the GTSS "In most cases, each youth member will be under the supervision of a parent or guardian. In all cases, each youth participant is responsible to a specific adult."
Your son was responsible to a specific adult, your friend. There are plenty of times when neither of Jimmy's parents can go camping so Johnny's parent says "I'll be responsible for Jimmy." And of course you can have one adult responsible for more than one Cub or else siblings would almost always be out of luck.
As an registered scout leader youth protection is very important. 17 years ago while I was Cubmaster I was at a Council run cub scout family campout. There were 4 or 5 other families from our pack set up in our campsite. At that time I had only met each one of these families just several months before when there son joined the pack. About the time I was going to start cooking supper for my son and I, I received a phone call from my wife and was informed that she, my mother and daughter had been involved in a bad car accident. I informed the parents of my pack of what had happen and that I was going to have to leave. Where my automobile was parked at the camp there was no way I could leave in it without having several autos moved and no way of knowing who they belonged too. Another couple that son was in another pack who I knew very well since they lived on the same street that we did and our sons played together with offered to carry me to my home 10 miles away from the camp so that I could go to the hospital in our other vehicle. They offered to watch my son so that I did not have to take him with me. I made the decision to leave my son with them since it was the only option I had except for taking him with me.
I broke the cub scout camping rules when I allowed my son to stay over night at the campout without a family member being present at the campout. Would I do the same thing again today in the same situation, yes I would.