You're right Laurie, the way we have planned it makes 1,000km.
Doing the Baztan backwards cuts out ONE bus trip - if we went the "right" way, we'd need a bus up to Bayonne and then another from Pamplona to Saint Jean - this way saves one of those trips! It saves some zigzagging too and makes for a loop instead.
Canuck, your suggestion makes perfect sense - in fact it is originally what I was planning on. The one deciding factor for me was lack of accommodation, especially when FatmaG posted information about readily available cheap albergues along the Baztan way.
But as I say, when I looked at the map, I wondered why we were taking a bus to SJPdP and am now even contemplating "just making sure" I couldn't find cheap enough accommodation along the Nive!
Don't fear Laurie, I've spent so many hours poring over googlemaps and your translation that I HAVE to walk it now!
Even if we did leave it at Larressore, that last stretch into Bayonne seems to be all along the riverpath so I'm sure I could add nothing to your instructions!
Maybe our 1,000km could just end at Melide!