You mean alt-coins. As you know crypto-market is decentralized and unregulated so anyone with a new idea and technological backup can develop its own coin either by creating its own blockchain or on ETH platform. So if a coin has its own blockchain, it is not FAKE.
But question rises about its authentication, a lot of new ICO's are launched every day but most of them came out as a scam at the end. We should check the background of the developers of these ICO's to validate its authentication + the purpose of its development. If both these things are up to the mark then the coin is authenticated.