Order of Magnitude
The leave side had Boris’s battle bus which had the slogan “We send the EU £350 million a week, let’s fund our NHS instead.”
While it is technically true that the cost of the UK’s soon to be ended EU membership is £350 million per week, we got a rebate (i.e. a discount) of £100 million so we only sent £250 million per week. While it is not stated in the slogan how much exactly extra money could be available for our NHS, it cannot be £350 million per week, since only £250 million per week ever existed (to the extent that money exists).
For me, the question of whether to be in the EU or not was never about money but the slogan would have worked as well with whatever the correct fact-checked figure is.
However, if it was meant to be a trap, it worked. The remain side had far more money and far more establishment figures, and when it constantly sent those figures out to say that the real number is really £250 million per week and some of this is spent on useful things here in the UK etc, it is made leave’s case for it.
For £250 million a week is still a massive number and the same order of magnitude, by focusing on the detail, Remain left the overall premise unchallenged.
Having your opponents make a point for you, frees up your own resources and own airtime for other points.
Not that it matters, as no one was listening. People voted for their own reasons not because of anything Boris said.