I just have some general comments for what they are worth.
I have definitely found that my less expensive
e down bags and garments leak down more than the higher end brands.
I wanted to make a down "elephant's foot" (a short bag for emergency bivvy to be used with a down parka) at one time and I was going to purchase a down comforter at a thrift store just for the down.
I found a better source, but that is another story.
We had a down comforter that after a year shifted the down completely away from the center and it was easy to see holding it up to the light. We took it back to Kohl's and they replaced it and said the quality control in some cases was very poor and blamed that. I, like you, couldn't figure for the life of me how the down moved because the baffles seemed to be intact.





BTW, I have a couple of decades old down bags that still work fine (but are heavy) in spite of their age, but it sounds like you use them infinitely more than I ever do. Are you writing anywhere about your travels on a bike? Sounds like and adventure to say the lease. I might consider that, but it would be a bike with a gas engine!