Here's my take on the 'Walker' problem. The Bodl has him finishing in 1834 because that's when he died/retired (not sure which) but his son, George Walker Junior then continued the business. Somewhere I have the 1839 catalogue of ballads obviously put out by his son. Walker jr was at Sadler Street, Durham from 1834 to 1886.
Addresses might help with dating. The father was at 'Market Place'.
The father was also at 'Claypath, Durham, c1827-28. Stock numbers used by Walker can also help, and associate printers like Livesey of Manchester and Williamson of Newcastle. He may also be related to William Walker printer of Otley, not a million miles away. There was also a William R Walker printing in Newcastle c1856-67 who may be related. Just to confuse the issue further there were also contemporary Walkers printing in Preston, Bradford and Norwich!!!