Complex sentence: Although no customs records or other documentation of port traffic relating to Helston survives, such records do exist for Gweek dating back to the 12th century when Helston had jurisdiction over shipping for both Helston and Gweek.
Split into simpler sentences: Although no customs records or other documentation of port traffic relating to Helston survives, such records do exist for Gweek. Some of these date back to the 12th century when Helston had jurisdiction over shipping for both Helston and Gweek.