If a case hardened receiver is annealed, is it the whole receiver or just the thin hard case that can even be annealed. Didn't case hardening come about because the iron or very low carbon steel that was readily available, could not harden on it's own.

Also could be that if a receiver is permanently bent, it was deflected to a point that was exactly the same regardless of how hard it was. It may be that a classic receiver that was unable to harden, except for the created case, was less likely to crack than a through hardened receiver. Maybe?