The problem with Chain of Custody, and Deeds filed at the County Courthouse, is that they are based upon the idea that the information they contain is correct, and this is not always the case. All my deeds are warrantee deeds, not quit claim deeds, and when I buy land, I do go back 100 years on the title search. Still, it does not catch all the mistakes. Sometimes information is just not carried forward.
In my situation where my neighbor sold my land, which is just a few acres luckily, the land was won in some lawsuit, in the mid-1800's. The land went from a landowner in one town, to the abutting landowner in another town. No big deal, and for each change of ownership, the deeds conveyed the extra land in the opposing town.
Then it was left off mistakenly, and this happens quite often...
I keep saying that "my neighbor sold my land", but that is not really the case. I have always owned it, and still do, it is just that the person that buys it thinks those acres belong to him. They don't, my neighbor never had the land to sell. So it will be redacted.
But surveying is a real issue in 2020. In Maine anyway, there are not enough surveyors anyway, and they charge entirely too much. I had just ONE line surveyed, and it cost $600...and they never surveyed it right, nor all the way to the pins. But I own hundreds of acres of land, in (5) towns, and (2) states...there is NO WAY I could afford to have it surveyed. So you rely on the surveys that were done from years past...
Your neighbor's issue is with the title company, not a surveyor. Although it would probably take the latter to straighten it out... as I said before though, I don't know how they can survey "one line."