They do know because there has been at least one court case fought about it, they just don't want to admit that they knew ages ago (2014) that there was a problem but did nothing about. Ross Anderson (Professor of Security Engineering at Cambridge University) did an analysis of the tags and presented evidence about them as an expert witness - his analysis of the tags was not favourable to the government's case. See here: https://www.lightbluetouchpaper.org/2014/12/13/curfew-tags-the-gory-details/
Biting the hand that feeds IT
