If you have the original key from that tube it should align to the tube like a puzzle. IOW, there should only be one way to attach it back. At least that was the way it was with my KT88 that had the same damage. However I can see that the 6sn7 would be more challenging. Mine are all stamped the same BUT they are new not NOS. If you cant be sure the its cheaper to chuck it than repair the amp from a defective tube
Broke key guide on 6sn7 how to keep using tube
I broke off the key guide on a black glass Sylvania vt-231 and a black glass RCA while using a Garage 1217 tube adapter. The key hole is very tight on these adapters and so are the pin sockets. I know the tube is still good just don't know how to orient the pins withe correct socket holes. If I can figure this out I can just use a paint pen on tube and socket for the future. There are no numbers in the bottom of the tubes so where do I go from here? I have more of these tubes but hate to throw in a junk drawer. Thanks for any help.