The transmission circlips act as stops for certain sliding gears and even with the crankcases split, they stay in place. The countershaft & mainshaft in the transmission have to be disassembled before the circlips are free.
Roger that. Thanks. I have an inquisitive mind and am intuitive by nature. So now my curiosity is piqued and my intuition is in active mode.
This bike "came to me" in an unusual set of circumstances as I bought it from an estate after the previous owner passed. Thus far I like the bike and am very pleased with the ride and handling, but I was unable to query the PO about his knowledge of the mechanical history of the bike.
The upshot is that I towed the NT home for ~ 500 miles on a trailer, so it had plenty of shaking and bumping on that trip. And I've owned the GL18 parked next to it for eight years and nothing has ever fallen out from under it. So this had to have come from inside the bodywork of the NT.
Which leads me to several questions:
- If I found this on the floor, and they are only installed inside the transmission, why was it stuck somewhere in the bodywork?
- If this indicates the cases have been opened, how might I find out what Honda shop did the work?
- And finally, if it has a transmission issue, what should I feel or listen for?
Ah ... the joys of purchasing a new (to me) motorcycle. My wife and I joke that any new mechanical conveyance is just the "starter kit."
A little used oil and a couple spare used nuts and washers can go a long way! 
