I do not know about people fiddling dates for tax reasons, but i do remember that DS was a fortnight overdue and I was taken into hospital on a Saturday morning to be induced and by Monday evening he was still quite happy where he was, although I was getting a bit fed up, when I suddenly realised that if he wasn't born until Tuesday I would get another weeks maternity benefit and decided that after all the trouble he was causing, he could at least hold on where he was until midnight had passed so that I would get the extra cash.
He did and so did I.