Time Warp?

Do HM Revenue & Customs work to a different calendar to the rest of us?  TJ has just received this tax notification letter for the period 6 April 2018 to 5 April 2019:-)  What is the point of it, when tax has been deducted for the last ten months on the previous tax code?  There will be a Budget in March when everything will change and they will have to send out another letter!  Is it to keep them all in work?

And after all that, the figures are wrong, as always!!