] I guess that leaves an opening for some imaginative writer to declare that Lief Ericsson's second in command was actually named Darcy the Dangerous......;-)

Could be. According to Vivian King's The D'Arcy Pedigree (1901) William, earl of Arques (d'Arques), had his residence at Dieppe. His son, Norman D'Arcie (b. 1050), who would have been first cousin to the Conqueror, was made Lord of Nocton. Coming down about eight generations, to circa 1400, Margaret, daughter of William D'Arcy, married Steven Fitzwilliam, 1405-1450.