If there's a new dog in the area it could very likely be that dog the note writer is hearing.
My dog, who very rarely barks, became very vocal when we moved into our current house two years ago.
She soon settled down once she got used to the new area.
Where I live I'm surrounded by dog, some of whom bark a hell of a lot and apart from the dog next door, that does bark a lot, I really couldn't say exactly where the rest of the barking is coming from: it could be from behind my house, or down either side of the road. It's just general barking and it's impossible to locate.
Sounds like a very good idea to get all your tech in place and then you can be absolutely sure whether it's your dog or not.
And as pp has said, don't worry about the RSPCA, they won't be in the least bit interested.
And as for the council, it would be treated as a nuisance noise and the person complaining will have to take recordings and log times of the nuisance and show that it's coming from your house.