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The main disadvantage is that you cannot query the owner of NFTs on-chain. And there is no way to enumerate tokens on-chain.


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In general the answer is no. ERC721 is not more gas efficient for minting NFTs. However, you can put whatever you like in the mint function so this will not always hold true. If by "identifiers" you mean state storage for tracking then no ERC1155 also doesn't require more "identifiers". I wrote about this in depth in this stack overflow ...


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It's not possible. NFTs aren't like wallet addresses which are unique globally. NFTs only make sense in the context of the contract that created them. Inside the contract, each token has an id that normally starts counting from 0. So NFTs minted in a contract live forever in that contract. Check https://github.com/OpenZeppelin/openzeppelin-contracts/blob/...


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