You cannot really rely on the FCC listings for accurate RR frequency usage.
The larger railroads often do not have specific licenses for mobile frequencies used in an area and I have seen numerous times where frequencies included on a license are not used in a specific area.
There are two railroads operating in Allegany County, NY.
The Western NY and Pennsylvania RR operates the east/west line between Hornell and Olean. I have frequencies for this RR listed in the Railroads section of the Pennsylvania database.
Norfolk Southern operates the line running NW from Hornell to Buffalo (referred to as the Southern Tier Line). Some of the frequencies listed for Norfolk Southern in the Pennsylvania database would be in use in the area you're asking about. 160.800 is used as the main channel for the Southern Tier line as it runs through PA. The frequency changes somehwere in NY if I remeber correctly, but it changes to one of the three other main road channels listed under the NS Harrisburg Division.
Pennsylvania DB, Railroads Section:
http://www.radioreference.com/apps/db/?aid=3166