Sounds exactly like what I said, but with twice the words and therefore probably twice as clear :)

You wouldn't necessarily know about the problem from a survey. Unless there was already an indication of the possession (a fence with occupation up to it) apparent to the surveyor, the survey would only show the record line and you would have to wonder for yourself why the line on the ground (if it was marked out) didn't match with the row of bushes. A row of bushes doesn't make it onto a survey unless it's already being looked at with interest, and is being noted intentionally. Not to say that getting a survey when buying property isn't money well spent, it is, but it wouldn't necessarily alert you to this issue.