They have just been issued nearly two years after the Queen's death, but in order to save costs and limit climate change they will largely be swapped one-for-one when the old notes become unusable. Unfortunately we will have to go through this process once again when Charles dies and William takes over.
The thing is, why do we need the monarch on the notes at all? The BoE issues these notes on behalf of the UK. Why not have famous landmarks on the notes from all the countries of the UK: The White Cliffs of Dover; Snowdon; Edinburgh Castle and the Giant's Causeway or similar?
They could be churned out year on year regardless who was on the throne.