The survey is probably right. Many times people will intentionally build fences well within their own property. Or the person building the fence may have been guessing. But a fence line that has been historically used as a boundary will hold up in court.
Half the old fencelines in alabama were never surveyed it was just guess work. They should go off what the deed says. Just because grampaw put that fence in 30 yrs ago because he thought it was the line in my opinion doesnt make it right for someone to try and claim it now.