Well, actually, I think the Fourth Doctor had eight too. Sarah, Harry, Leela, K9, Romana, Adric, Tegan, Nyssa. Unless Nyssa doesn't count because her first story was the Fourth Doctor's last. But then I could count Romana twice.

But anyway, three quarters of the First Doctor's companions qualify.

One third of the Third Doctor's companions qualify.
One eighth of the Fourth Doctor's companions qualify.
And one half of the Sixth Doctor's TV companions qualify. (Evelyn is definitely canon in my world)

Stop making me do maths!