What is the difference between NFC (ISO 18092) and Contactless Card / RFID (ISO 14443)?

Has anyone tried to embed an NFC chip like MiFare DESFire or even simple NFC tag into a dumb watch strap? Then you could potentially unlock office doors with your dumb watch - should be a bit easier / faster compared to pulling out your thick wallet with Access Cards in it, and it could have potentially some other applications too.

Can you stack multiple NFC cards on top of each other in your wallet? Will they continue to work without interference? Or will they block each other? I am just being lazy and do not want to pull cards out of my wallet to open various office doors, I just want to touch the reader with the wallet and be done with it. And the wallet of course would contain several NFC cards held pretty close together. Can somebody please stage an experiment an

Who manufactures smallest NFC tags?

What is the size of the smallest NFC tag?

Are RFID Glass Tags compatible with NFC tags / readers?