Have spotted those two IGI entries myself in the research, Susie looks the best bet at the moment. There is also another Humphrey Sykes I've come across who is a Hatmaker not a Bookkeeper, born Slaithwaite 1806. From 1841 - 1881 living Bury, Chorlton and Hale areas of Lancs/Cheshire. (Grace was married in Stalybridge). This Humphrey married Ann Varley 1830 which is after Grace was born in 1820 (not impossible I know!) and their seven children are born between 1833 - 1852 so it's not that convincing.