Indeed, but as GSR 800 comments, the Enterprise worked differently. One particular feature was a shutter in the bar, which was moved across at the border to shut the ‘northern drinks cabinet’ and open the ‘southern’ one, thus ensuring alcohol was sold at correct duty rate in each jurisdiction! The only other train, I think, which crossed the border without checks, was the Bundoran Express, which avoided checks by not stopping at any stations in NI. Would have been a fine sight running round the curve of Enniskillen station.