Why the nil rate band IHT is available in example 2 in the opentuition notes

Hi, Earlier illustrations show that nil rate band will be reduced by the amount of lifetime chargeable transfers on death, and only the reduced nil rate band can be used as an allowance to calculate the death estate IHT liability. But in example 2 after section 9 (The 7 year cumulation period), the nil rate band was already used up when we calculate the lifetime chargeable transfers on death for the PET made on 1 Sep 2015? Why is there still full nil rate band available for the death estate liability calculation? thanks.