I am so, so sorry what you are going through.
I think the number of conspiracy theories laid out here is laughable.
OP, I'm sorry people have to complicate things.
You bought what is almost certainly an authentic bag and had it authenticated by the top authenticator in probably the world.
Authentication by photos is different than by hand but there are tells.
The fact that your bag went through three levels of checking at HQ means they themselves were unsure. Whatever it is they are seeing or not seeing is probably an anomaly in your authentic bag.
I am not sure I believe there are many, if any, people left at Hermès whom I'd trust absolutely in authenticating a bag more than ten years old. I certainly don't trust H unequivocally in these matters.
The odds of anyone special ordering a sellier Mou from a super-fake manufacturer with that date stamp, etc. - I won't go into detail but the evolution of the superfakes makes it very, very unlikely.
You have an owner of the bag, a trusted reseller, an authenticator/world-class collector, and a new owner of the bag, all but one of whom have held the bag in their hands and all of whom feel it is authentic.
Of course it is all possible - a superfake Mou that slipped through this many experts. It's just very, very unlikely given all the above.
I'm hopeful the previous owner of the bag will be able to find you a paper trail that will support you. We are all (ok, most of us apparently!) still pulling for you and your Kelly.