Interestingly, that was (allegedly) because the Guardian was printed in Manchester, and therefore had to be delivered to London by train overnight, meaning that in London (where most of the press and other media who could write jokes about "the Grauniad" were), the copies would be earlier editions that had more mistakes in the highly manual typesetting and proofreading process. The London papers, printed in London, would use the more-corrected later editions for distribution in London.