I bought an apparently new DeWalt DCD995. Couldn't remove the chuck, like
it was welded to the spindle. Then I bought a DeWalt DCF899 so that I could
properly remove a chuck.

Then I bought another 995. The code on the battery holder is "DCD995-TY3
2015 39-41".

I went to remove the chuck with my 899. Obviously something was going to
come off. Unfortunately, the drill broke and the chuck did not come off. It
would be understandable if these hammer drills were refurbished, a hammer
drill probably welds the chuck to the spindle after some serious use or
testing. Could that drill be refurbished?

Yes, I removed the reverse-threaded screw first.