There are 2 other ratchets on alloy artifacts with forge codes on them, both different, and different from the [CH] mark. So my assumption would be that Cornwell was contracting out ratchet production in the early days.
Your ratchet does not have a hole in the handle, so it's not a #55 and it's not one of the SR series.
Does your ratchet click when turned?
As for age, weakly, the contract stuff seems to be in the 20's-30's, but you may have an unknown Cornwell ratchet that predates the #55.....
[You also have the only other ratchet I have seen with the CH forgemark besides the CM&D ones]