Spock and Jim share clothes so often that by the time the TOS movies take place (or at least the later ones, like after Search for Spock) they genuinely cannot tell whose clothes are whose.
Well-- theoretically, anyways.
Spock says he doesn't remember, but he does.
Jim has yet to question how his husband, with his nearly perfect Vulcan memory, cannot tell whose clothes belong to who. In reality, Spock just likes seeing Jim wearing his clothes to official meetings and such without realizing it now that they have the same rank-- their uniforms are basically interchangeable at this point. Plus, Spock would never lower himself to the point of purchasing a sweatshirt of his own volition-- unlike his husband, who hasn't seen any of his hoodies since he graduated the academy since Spock has been stealing them for years.
So, we know that Kirk is given glasses by Bones on his birthday at the beginning of Wrath of Khan.
And then in Voyage Home he sells them in the past, but in this exchange with Spock -
Spock: [Excuse me, Admiral. But weren't those a birthday gift from Dr. McCoy?
Kirk: And they will be again, that's the beauty of it.
- it is implied that this is a closed loop, and it's all fine. (yes I know it's a paradox in itself but it's a loop so I'm giving it a pass)
HOWEVER:
Kirk his given unbroken glasses by Bones (obviously), and then they get broken, meaning their first (second?) appearance in the past, at the antique shop, is with a broken lens.
Therefore, at some point, someone has fixed them before Bones gifts them to Jim.
But that means that different glass is being passed around the time loop.
Previously I'd imagined a time loop like this:
But upon realising this, the actual lens' journey through time is more like:
And my brain likes infinities not enclosed in loops FAR LESS
But anyway, here are my ramblings for the day. Enjoy?
(I realise infinity signs and glasses look kind of similar no visual pun intended, or indeed confusion!)