The 12 investigations announced are the first twelve to be worked on. The inquiry will look at any and all abuse involving children over any time period Justice Goddard and her team decide is needed.
edit: "These 12 investigations constitute the first phase of the Inquiry’s work and further investigations will be announced as the Inquiry progresses."
https://www.iicsa.org.uk/investigations
There is also a charity commission investigation into JWs as a whole in Britain, as well as two into specific congregations.