It isn't a big deal, but there are two versions of Part #17 which is described as a "Gear Ring."
The newer reels have a single knurled ring or cap while the older reels have two flat rings with a notch in them. I don't know if the parts are interchangeable, but I have a couple of 50A's and at least one of them has the older two rings while the other has the newer #17N ring.
FWIW - I had to fabricate a tool to get the older #17 pair of gear rings off of my older 50A when I cleaned it, while the single #17N ring is easy to get loose and remove.
Coincidentally, I also use the Orvis reels on bamboo spinning rods, not surprisingly on Orvis bamboo spinning rods of which I have a nice assortment. I have been looking for an Orvis 100 for one of my rods which dates to 1947 but to be honest, I have a really nice half bail Mitchell and a #2 Hardy Altex that are more age appropriate.
BTW - I did a full strip and "Bulldog cleaning"
on my Orvis 50's, and the Mitchell & Altex with no issues and excellent results!!
Good luck & enjoy!!