Legal Question in Real Estate Law in California

I do not see any facts or know of any theories that would transfer land from Parcel A to Parcel B. Each parcel remains the size and shape shown by the records down at the County Recorder. There is no adverse possession, prescription or agreed boundary case here. The new owners of parcel A are entitled to the land described in the records, not the land as delimited by the fence.

They don't even have to ask for the land back. They can just tear down the fence if they want. It's on their property. You can't change a lot line location just by building a fence, especially when you own both parcels. When you own two adjoining parcels, the only way you can move the lot line is by obtaining approval for a lot line adjustment from the city or county the property is in, and then recording a new parcel map and legal description for the parcels.