I don't know if it was still the case in the late Victorian period, but in the early 19th century when the likes of Peter Stubs were doing rather well in the Lancashire tool trade, there was a strong pattern of tools being made by small scale outworkers, known as "country hands." Tools were made in cottage workshops then gathered in to a named "manufacturer" who inspected them, marked them with his brand and sold them.
If Thewlis was using this system, their works could be far smaller than would have been needed for all the tools sold with their name on.
With Stubs, whose fame rested on files, only saw files and clock hands were made in their own workshops. All the rest of their range - other files, clock parts and general tools (including pincers) were made by country hands.