Inheritance tax

If a person dies on 1 April 2022 and IHT payable gift on lifetime gift 10 Dec 2018
Why it says no lifetime inheritance tax?

Life time transfer of value of £55000 in 7 years to a trust before 10 Dec 2018 (transfers after 10 December 2011) .Nil rate band 325000-55000 =£270000 available to compute death tax.
Why it’s written in bracket(transfers after 10December 2011)

And under IHT payable on death estate
No life time transfers of value in seven years before 1 april 2022 (transfers after 1 April 2015.) Nil rate band £325000 is available .
Again why it’s written in bracket (transfers after 1 April 2015)
Why it’s written no life time transfers of value?

Many thanks ?