1st source is by Phillip Cohen who's an expert on South Asian studies & did extensive fieldwork, interviews for this info & his book states Rahmat & his team coined it. The 2nd's Rahmat's secretary (contemporary source) who said he coined it. More sources claim Rahmat coined it.
It is important to remember that the name βPakistanβ was 1st coined by Khawaja Abdul Rahim Kashmiri & subsequently adopted by Chaudhri Rehmat Ali.