That wouldn't make any difference here at all. The author already has proof, signed by the postmaster of his post office - that's a very very high bar legally

That wouldn't make any difference here at all. The author already has proof, signed by the postmaster of his post office - that's a very very high bar legally speaking BTW, you'd have to get a judge to sign something to carry more weight - and Amazon is ignoring it. A blockchain based delivery confirmation system could be ignored just as easily as this...