@sreevesjc its at best a four day walk. Just keep the sun behind you and you'll get there
There will be no way-marking for the reverse route. Turismo Galicia have no reason to provide. Not so much of a problem if you've walked from Ferrol first, the route(s) are fairly obvious, but you ain't. Any of the Camino apps with the GPS blue dot (or just Mapy.cz, plot a route to, and your daily destination) will get you there and I guess you're under no compulsion to follow an "official" route.
We are planning Ferrol / Santiago / A Coruna but have no intention of following the "official" path any more than we are physically obliged to. We are going "old school", that is we are going to join up the places that welcome wandering travellers with shelter and food and aren't necessarily "en piste". We are going to sneak up on the Old Boy and shout "Boo!, you didn't know we were coming". And I'm looking forward to poking about in bits of Galicia that don't spend their days playing "one peregrino, two peregrinos, three peregrinos, four, five peregrinos, six peregrinos, how many @$£!ing peregrinos? More?"
Buena suerte