Webley MK V markings and some doubts

[PeterOM]

I bought this Canadian marked Webley MK V about 5 years ago and while doing some research I see it doesn't have the serial number on the edge of the cylinder. The last three digits '833' and '455' are on the face of the cylinder (see pics). It doesn't appear to have been shaved, the firing pin touches the primer on a spent case. Any ideas? Thanks, Peter