Two NFT listings both show token number 42. That does not mean they refer to the same asset. The number has meaning within a particular contract, and the contract itself must be located on the intended network.
The ERC-721 standard defines a unique token identifier within an ERC-721 contract. A token ID by itself is therefore an incomplete reference when comparing assets from different contracts or chains.
Record the identifier as a combination
Keep the network, contract address and token ID together. A marketplace title, collection name or thumbnail is a display label, not a substitute for that combination. Similar names and images can appear in unrelated contracts.
When checking a listing, follow the contract details through a trusted explorer for the correct network. Do not assume that matching token numbers prove matching ownership, history or rights. The same number can be valid in many separate collections.
Large token IDs should also be preserved exactly in notes and software. A spreadsheet or programming environment that silently rounds a large number can change the identifier. Treating it as an exact text value is often safer for a human-readable record than letting a general-purpose sheet guess its numeric format.
Separate identification from other claims
Identifying a token does not establish that the artwork is original, that a seller has broader intellectual-property rights or that a purchase is worthwhile. Those questions require their own evidence. The contract reference solves a narrower problem: which on-chain item is being discussed.
For an illustrative comparison, write “network A, contract X, token 42” beside “network A, contract Y, token 42.” The repeated number no longer hides the different contracts. A third record on another network needs that distinction too.
Use read-only inspection while learning and avoid signing a transaction simply to view basic identifiers. A complete reference makes records easier to verify and reduces confusion without implying that a correctly identified NFT is automatically safe or valuable.