I've just had a look at my own box set with 5.5 in it and it has the 6201 SKU number on it. The rulebook inside has SKU number 9101 on it but so has the 5th edition rulebook in my UK T&T box set. I had a quick look at the FBI website to see whether Rick has any old copies of 5.5 but it is currently listed as "out of print"
Sorry, I thought I was being helpful but having read this back, it doesn't come across as at all useful
I was at a bricks-and-mortar store the other day and there was a shrink-wrapped SKU #6201 box on the shelf. It felt kind of heavy to me. The guy working there said he did some research and assured me it was 5.5. I explained to him that if it wasn't then I was not going to be very pleased and wouldn't want it. He agreed to open it. Inside: Deluxe Tunnels & Trolls, paperback edition. Wow.