Yes, 1975 was the year detented UHF tuning (to make UHF as easy to tune as VHF) was required in all new TVs. I guess too many people complained about how difficult it was to tune in a UHF TV channel properly.
BTW: Today's flat screens, with all-electronic tuners (no knobs or dials to be seen anywhere, just up/down channel buttons) are even easier to tune--all you do is select the channel you want to watch and enjoy the show. No fine tuning required, ever. I don't remember if the detented UHF tuners had fine-tuning controls, though.
