Renfe is a bit of a law unto itself in terms of putting trains on sale.

The same message appears for that train for much of August, but it’s currently on sale up to the 6th.

I would keep checking with Renfe to see if they put it back on sale (start by checking for the second week in August), but also come up with a Plan B just in case they don’t.

You could also look at getting a bus to Valladolid or Miranda de Ebro (at your own cost) then picking up a train from there. Bus timetables at alsa.com

thanks ralderton!

Renfe have published a timetable to the European Timetable Centre and that's what DB, Eurail and others use. If reservations then can't be booked, Eurail will show the standard message you see.

However, as long as the train can't be booked, Renfe themselves either don't show it at all, or with a notice you've seen, that it's currently not open for reservations. Rail Europe doesn't show such trains at all.

thanks rvdborgt!