in fact there were / are dozens of other frequencies in use.
40Hz for one. Didn't one of our antipodean members say that was used in Western Australia at one time?
Yep, 256/440V @ 40 Hz was in Western Australia for a while, replaced by 240/415V @ 50 Hz. Adelaide had 210V @ 50Hz, now 240V & some remote cattle stations were 240V & 60Hz (ex-US Gov't gensets), now 240V @ 50Hz.