I run into 14g back fed switch legs on 20A ckts in older say 50's - 70's homes around here quite often.
It was explained to me years ago that they used to allow that and since the "true rating" of 14g copper is 20A before the derating applied by 240.4(D) I shouldn't freak out and change all the breakers to 15A. I'm still tempted to.
I can't imagine why someone would actually require it done that way.
It's also common to run into really old fuse boxes protecting 12g K&T or cloth and paperwound cable at 30A and it seems it was installed that way by the original installer.
On another note: I can't find article 219 in any of my code books.
