It's a good question. In practice, a project will publish the official contract address and the chain on their web page. Hence, it becomes a schelling point fo

It's a good question. In practice, a project will publish the official contract address and the chain on their web page. Hence, it becomes a schelling point for users. It assumes that the project owners are in control of their servers and DNS. For users, there is then just one official contract, regardless of how many others are published and on different chains. As an aside, there is ENS, which people are starting to use to say they own a DNS domain https://docs.ens.domains/dns-registrar-guide https://docs.ens.domains/dns-registrar-guide. ENS itself is an NFT, so it's turtles all the way down.