Re: Imperial Potentate. Bred in Australia (1921) by Alister Clark. Not Alister Clark. This rose was bred by Clarke Bros., Portland, Oregon. Bobbink & Atkins 1932, page 16 say in 1923.
Yep - not one of Alister Clark's roses. Re the reference to the 1923 date of introduction, this must have been a typo too as it had been introduced from America to Australia by 1922 - The 1922 Hazlewood Bros (Sydney, Australia) catalogue lists it in the 'Novelties for 1922' section, described: IMPERIAL POTENTATE (H.T.) (Clarke Bros.). - Dark rose pink, slightly lighter on reverse of petal. Flowers large, full, high centre, on long, strong stems, and fragrant; mildew-proof. ("abridged description from raiser's catalogue".)