I stayed at a couple of places that Correos did not list. I phoned them up and they asked that I get confirmation from the accommodation that they accepted bag deliveries. In one place they said it was shut when they arrived and they delivered to a different place but told me where my pack was. It turned out that where I stayed had a side door so in the morning I sent them a photo of the door and they were happy with that and picked up my bag. I did find them very helpful when I contacted them by phone and they would pass me to an English speaker.
Here is what they sent me:
In order to add an accommodation that is not on our list to a reservation, it must meet at least one of the following requirements:
*Reception service from 8:00 a.m. to 2:30 p.m.
*Access code - so that our route staff can access to drop off/pick up suitcases.
If the accommodation reception service time does not cover the requested time, it cannot be added. Additionally, please note that the delivery staff does not undertake to make phone calls to the accommodations before the service there.
If the accommodation confirms the reception service or the access code, you must send us the name, address and contact telephone number of the accommodation, in addition to the access code if applicable. After that, we will confirm whether or not it is possible to add it to the reservation.
We are waiting for your instructions.
Best regards.
AVISO LEGAL