If you like your neighbours at all that are giving up some of their land to this, give them the heads up as to just what a pain in the ass it can be at selling time.
It does delay things if there are complications with boundaries.
OP, glad you are on the ball.
I have a friend who bought a probate house and discovered that the neighbours at the back boundary took up to 10-15 feet of a long old garden and built on it.
It was awfully stressful, they were so pissed off as it was a really dishonest thing to do. But she was pregnant, parent dying and they didn't have the bandwidth for it.
About 15 years later the neighbour is trying to sell and they have the energy and they contact them that they want it taken down and their land back. Just one legal letter to them and a copy to their estate agent letting them know they will be taking action.
It messed up their sale and they were in complete stalemate for months. They had the cheek to be pissed off they were kicking up a fuss after all this time.
Eventually they accepted a generous payment for the transfer of ownership.
Take plenty of photos.
I could give you half a dozen CF stories where people have chanced their arm doing this.
You would be amazed at how many let it go for various reasons and they get away with it, its why they do it.
My friend had a old lady living next door who went into a nursing home.
After about a year in she noticed her garden being interfered with. Someone on their boundary thought it an opportune time for a land grab.
She contacted her family and they were around and stopped it.
But not everyone has family to step in.