Bracton has some very cool correspondence with Mr. Leiber, that he could have compared, but anything of this sort would be sheer speculation with definitive proof highly unlikely. So personally I was glad that the seller did not get a bonus for speculating that it might have been owned/written on by Mr. Leiber.

Since it was mentioned, I do have some original Fritz Leiber correspondence.  While I'm certainly not a handwriting expert, the writing on the letters I have doesn't look anything like the handwriting on the cover of that Chainmail.  Probably a good thing that a premium wasn't paid for it.