because it's an enormously wide question!
It would have been easier if you had asked limited.
Rare could have been produced in several thousands,
as this poster I have, but which there are left still very few left of,
and which I can't show you, because the site isn't rarely(!) not working, get it ?
This site's posting of pics have been working 1.000.000 times, at least,
but to show how rare it is, it has to show that it does not work now !
So rare should not be confused with how many that was produced from the beginning.
Rare is how difficult it is to achieve an object now.
Of course most vintage VC's are rare,
because they were produced in very small series from the beginning,
and therefore few are at the market.
It could also be, certain objects that are so beloved by their owner, that they don't sell them.
Rare could be one of the most produced cars ever, an old VW,
because, as all that once owned one, knows they disappear in rust!
Of course I know some few watches, that were rare from the beginning,
since it only was produced one unique example of them
Rare is also the utmost friendliness, comradship and egagement,
combined with humor at this site, Hour Lounge