A model release is a contract in which a model consents to the use of his or her images by the photographer or a third party. This applies not only to professional models but also to anyone that is portrayed in an image or a photo.
The photographer is responsible for documenting the model releases and must be prepared to send the documents to buyers if requested. The releases are not in need to be uploaded to Mostphotos by the photographer.
When you publish a photo with a recognizable person or trademark and mark it as commercial royalty-free, you have stated that you in fact have a release.
If you disregard model releases you are acting fraudulently and in clear breach of the legal agreement.
Contact firstname.lastname@example.org if you have any more questions or need any help.