hey laurie!
I did some of these this, er, last year.
01, por Jaizkibel: the first climb from where the official route goes left onto the forest road can be a bit dodgy in rainy weather. it is very steep and grassy, so slippery. it was wet and doable when I walked it. after the high point with the fortress, there is a section just above the cliffs on the left that can be unpleasant and the scramble down the rocks to the path needs a bit guesswork, but you can see when to continue. the rocks can also be a problem if wet.
01a, climb from Pasai san Pedro: it is possible to climb out of the town by the church then a series of paths starting at the far end of the cemetery to the road that circles the estuary to the lighthouse. If you are interested I can provide a more detailed description.
02, before Zarautz: if you round the camping site on the left, there is a fine local path (mostly paved, unfortunately) with beautiful views of Zarautz that descends to the beach, then you follow the wooden beach walkway into town.
03, Zarautz - Zumaia: after the climb from Zarautz you can opt for GR-121 directly to Getaria. it should be mostly on tracks and paths and is shorter.
03, Zumaia - Deba: again, GR-121 leaves Getaria by the flisch cliffs on paths and lanes before joining the Norte to the picnic stop. GR then takes a path from the picnic spot (not the road, as the Norte) to Elorriaga. the descent to the sea on GR has two unmarked intersections but it should be easy enough to guess its course. maybe that have been corrected already (I alerted the Deba TO). this is spectacular but often very steep and super slippery in the rain. there is a water pipe at ermita santa Catalina.
06, Lezama - camino after crossing the motorway: there is a path called PR-BI 250 Senda Uxinas that can be taken to avoid the slog into Zamudio. it was not (yet) waymarked with yellow arrows in August. it can be reached by turning left at the second roundabout after Lezama (the one after ermita san Cristo), under the railway and it starts at the following roundabout.
07a, Portugalete - Pobena: a spectacular route is to follow a combination of paths via but below the top of Monte Serantes. I can provide description if you are interested.
08, Pobena - Castro Urdiales: I had in plan an unmarked path alterntive from Onton to Saltacaballos but it was too rainy to try it. I did find mentiones of Senda Costera de la Minas that should start where the Norte crosses the river under the motorway before Onton then follows an old railway line (with tunnels) all along the coast to Miono. the start around the factory looked really faint.
10: is all on roads as far as I could determine, unfortunately. the yellow german guide has a recommended alternative from Laredo to the boat that passes a bit like this.
12, Santander - Boo: there is a doable variant from ermita Virgen del Monte to Mar, about half of which is on gravel tracks/roads. one unauthorised railway crossing (former road, now blocked).
15, La Franca - Llanes: the start of the alternative along the coast was well waymarked but the arrows soon petered out and then it was a bit of searching and wire-hopping to Playa Cobijeru. from there it was ok, the route farily obvious but the waymarks placed quite uselessly. from Pendueles some yellow arrows, too. spectacular coast.
16, playa san Antolin - Ribadesella: E-9 along the coast is almost all on paths and, well, fairly okay waymarked. we lost it in Picones then had to road-walk to pick it up again. we left it in Llames de Pria to sleep in Cuerres. but it continues all the way to Ribadesella.
17, Ribadesella - Villaviciosa: I would be interested in the first part from Ribadesella. that was too much road walking for my likeng. perhaps a bit shorter version could be to follow the norte to Abeo then connect with the suggested route.
18, Villaviciosa - Valdedios: it is possible to avoid the start of the Primitivo on the road by following the Norte further along the river Valdedios (a dirt track) then connect via tracks and minor roads to La Rivera and Valdedios. if you take a look at the satellite map, it is quite obvious. lovely route, much shade.
19, into Oviedo: to me it looks the official route. but if anyone has an idea for a less asphalt and less industrial route, I am all ears. that was one of the hardest parts of my entire camino.
