Aquí tienes, por escrito, la explicación del "auto renewal" y también el caso de un dominio transferido durante este período. Es un poco complejo.
https://www.icann.org/news/advisory-2002-06-06-en
Queda bien explicado en el último párrafo:
Cita: In summary, registrars should note (and advise their customers) that in most cases where a name is transferred within 45 days after its expiration/renewal date, the successfully transferred registration will only be extended by one year, not two years as might be expected. In such cases, the transfer during the Auto-Renew Grace Period simultaneously triggers a removal of the auto-renewed year and a credit to the losing registrar, and a charge to the gaining registrar for the year added to the registration term as a result of the transfer.