This is just a guess but maybe the "55" is actually 5.5 which is the Orvis Flex Index, rating for the rods flex profile.
I copied this from the Orvis Website.
"The Orvis Flex Index, which the company developed in the mid 1990s, describes the speed and amount of power required to make a rod bend to a predetermined load, and it allows Lepage to assign a numerical value between 2.5 and 12.5 to a specific rod action. The higher the number, the faster the rod action."
I believe that the Orvis Ultrafine rod, is a 7'9" 2 weight, full flex rod, rated at 5.5.
That was it. when I enlarged the picture of the rod, there's a "." between the fives. Never would have noticed it if I hadn't been looking for it. Thank you!