Early blockchain collectibles
In the strict sense, an NFT is a unique 1/1 token representing ownership of something (art etc).
In common usage, however, it’s used to refer to any kind of tokenized asset, nonfungible or not, that is viewed as collectible & represents ownership of something more than just the token itself.
For example, semi-fungible Bitcoin collectibles were first popularized by Spells of Genesis, before exploding in popularity on Ethereum post-ERC-1155 standard.
The key point is that NFTs are ownable, tradable tokens that represent something.
The entries in these timelines therefore go by the earliest date where the NFT itself fully existed; it could be owned, it could be traded (except soulbound tokens) & it represented something.