Those first two don't show reproof marks even though the chambers have been lengthened. At least not that I can see.

I've seen Brit guns that have been reproofed without showing the reproof mark (also crown over R). But it most cases with those guns, it's somewhat academic. They've changed proofmarks often enough that if the originals listed only chamber length and shot charge while the new ones refer to tons or bars, then reproof is obvious due to the 2nd set of marks.