I could be wrong, but it looks fake to me.
It's either an old classic, or a 25. But it definitely is not a 21.
A 21 does not have the extra finger grooves, so it looks like a 25. Depending on how old this particular model is, there should be a letter and 2 numbers on each titanium slab.
The clip does not seem to fit into any cut out in the slab, and the groove on the clip does not look functional like a real Chris Reeve clip.
Like I said, I could be wrong. You might have received a very old classic..I'd suggest sending it in.