Yeah the BBC almost never repeated Doctor Who. I know there are the missing episode issues with the first two doctors but as Mike says I knew about Pertwee and early Tom Baker stories from the Target novelisations. They had plenty of repeats on air, especially in Summer, but they mostly did sitcoms that had just been aired that year (there’s a contract reason to do with repeat fees, they could show those twice before they had to pay).
I got cable TV before most people in the UK due to poor reception at our house and a channel called ‘Super Channel’* started repeating all of Tom Baker’s run from the start in the late 1980s. You couldn’t even get them on video as they slowly released those one story at a time in no particular order. Compared to now it’s amazing how difficult it was back then to see stuff.
*Super Channel was so obscure (although it was like a prototype UK Gold) that when I Googled to check the date it started I can’t find any reference, only a Canadian channel of the same name.