We completed the Salvador in mid April 2022 (through snow- but thats another story!).
I wanted to report about luggage transfer experience.
We are old, so had booked mostly hotels, and an apartment rental in Pajares. But we also did the Primitivo after the Salvador, so had a suitcase each with spare clothes and gear.
We arranged for luggage transport on the Leon side of the pass with Juan Morales, who took our gear from Leon to Casa del Embrujo, and finally the next (snowy) day from there to Pajares. (We were staying at the Parador in Leon, so taxied back from La Robla for an extra night there, went back in the morning to La Robla with our luggage on its way to Poladura).
His number is +34 620 99 01 79. He preferred to use WhatsAPP which worked great. I used a translator app to create the messages in English and translate Spanish. (and then had my wife who is fluent check them, and it worked very well). She read the replies and I know enough spanish to figure them out also.
We never met him in person, his compadre picked things up. But very reliable and dependable service, and reasonable when you consider how far the drive is and how remote some of the towns are.
He has a website,
moralesbus@viajesmorales.com
and email also;
moralesbus@viajesmorales.com
After the Pass, we had transfer on the Mieres/Olviedo side from Joaquin Moran.
He was recommended by the Hotel Albar in Mieres, which BTW is a wonderful alternative to staying in the student housing there. (The only place I've ever stayed where they hang fresh bread on your doorknob in the morning for breakfast!)
Again, all done by WhatsApp: his number is: +34 619 14 6726.
He took our luggage from Pajares, to Campomanes, to Mieres and finally to Oviedo; total cost of all that was only 89 Euros which was a good deal IMHO. Again, very reliable and responsive to What's App queries.
This may be more expensive than Correos, but the Salvador is a unique experience, we only saw 3 other walkers the whole time, so there is not a lot of demand. Given the difficulty of the walking, it was nice to have pack that only had the (much-needed) foul weather gear, food and water in it.
I just wanted to give a shout out to these folks who were very helpful. I suspect you costs might be cheaper if you can get a group together to share the taxi services, (but you'd have to talk to them about their rates.)
Buen Camino to you all. Enjoy the Salvador!
and there are now options! 
