Scripsit "Robinson Tryon" <bishop.robinson@gmail.com>
My guess is that the lawyers who drafted the GPL knew or believed that
the courts would interpret such a "written offer" like a coupon: you
have to physically (or electronically, etc...) have a copy of that
particular written offer in order to redeem it for the source code.
In order to _enforce_ the offer legally, one would of course need a
way to prove that it exists. But I am not sure that the vendor can
demand that such proof should take exactly the form of a photocopy of
the original document.