IIRC, and somebody please correct me if I'm wrong, 25Hz power was used even in residential settings up into the early 50's in some parts of eastern Canada.
In NYC up into the 70's at least, power for two of the subway divisions (BMT and IRT) was generated at 25Hz but converted to DC in the field. However, I very distinctly remember the flicker of the incandescent lamps in some of the BMT stations in the 60's, as these were operated from the unrectified 25Hz source. I do remember that some people claimed they could not see this flicker, but it was very obvious, to me, anyway.
As another trivia point, commercial DC power was still available to some grandfathered customers in parts of Manhattan until just a few years ago.