Old Unique New Service info humbly requested

A friend from work inherited two heavily engraved Colt New Service revolvers, by my hardly adequate google-fu I've found they were made somewhere around 1910-14, there is a stamp of a crown with numbers and letters below that I can't find anything on, according to my friend these were made for the British, they are in .455 Webley, if anyone can tell me anything else it'll be greatly appreciated.
I have recommended my friend contact Colt to see if he can get a letter regarding them.
https://i.imgur.com/eo2cDVz.png
https://i.imgur.com/f67n5fN.png
https://i.imgur.com/RQbkVJk.png
https://i.imgur.com/eJQaPB1.png
https://i.imgur.com/yxhLpg6.png
https://i.imgur.com/NbQNyyI.png

Older pre-1920 .455 elre lovers are not heat treated. Keep loads below 13,000 psi. Not to exceed 3.5 grains of Bullseye or TiteGroup in Fiocchi, Hornady or Starline 0.76" length cases with 260-265-grain soft lead.

My friend has told me that he's not planning on shooting them, I gave him the info on the Webley round just for his curiosity.

The letter E, from what I understand, means factory engraved. I read that it also might mean Exported. He has two of them? Very nice. How close are the serial numbers? Has he disassembled them to see if there's any internal marks, numbers, etc? (inside grips)
There's an auction house in Maine, Poulins, who might be very helpful in IDing the guns. You can email them with photos.
https://www.poulinauctions.com/

This video is on the Poulins site:
https://www.youtube.com/watch?v=itWK1IBa8C8

Thank you, very helpful.
The numbers are far apart but the engraving is identical.

To the right of that crown stamp in your photo is a "broad arrow", which is a British military proofmark.

In all likelihood, that gun was produced as a standard blue revolver for WWI service with the Brits and got engraved later down the line. Whoever did it took pains to preserve the proofmarks though. Just a wild guess, but possibly an English job.

Has he checked a .455 round for correct headspacing to make sure the cylinder hasn't been shaved for .45ACP with moon clips or something else? I sincerely hope I'm wrong, but from the photos it looks like the gap may be a little too large for the Webley round's thin rim.