Aye, until I started collecting them, they did seem like rarities of course, but they're out there.
Check out Greg Aloisio's collection on that FB page - he wrote a book on the 1918 which is an incredible reference guide.
https://rdgunbooks.com/shop/ols/prod...ed-300-printed

Blades can be refinished, though cold blue has a distinctive smell, that sometimes gives away a refurb.
The chemical process they used to black the brass is trickier to fake - these are all $1000+ knives now, so I am sure someone somewhere has worked out how to effectively fake a WW1 finish and age it.

Tastes, priorities and values change, over the decades and even centuries now.
My 1918 in the photo had it's original scabbard, which was awful BTW, replaced for a handmade leather scabbard, somewhere a long time ago, the leather is MUCH more practical, but man, I'd love an original for it, lol.