2 questions- 1 about Countdown to the Millennium and 1 about whats a set?

The first question is, are Countdown to the Millennium pins that were sold at Disney stores in 2000 tradable at the parks? The other question is that I read pins that are in a set are not tradable. Does that mean pins that are 2 to a box say for instance the Haunted Mansion ones that you dont know what your getting not tradable if you get doubles? They are part of a set of 8. Any info. or help would be great as I am a newbe at this. Thank you!

Second question first. When pin trading first started, they sold things like this:

or

Each number is its own pin, and the stars too. The rule was that all 4 pins should be traded together, because they wouldn't "make sense" to just trade a 9 or a tiny star. In practice, CMs took them in trade anyway. So that is what is meant by a set, not the mystery pins in boxes.

Yes, Countdown to Millennium pins are tradable. They are metal pins, that have copyright Disney on the back. However, some CM's only know the Mickey waffle backstamp with the Official Disney Pin Trading logo, and will reject a pin that doesn't have that on it, because they don't know older pins had different looking backs. If that happens, just trade it to a different CM.

Thank you so much for the info. hopemax!