I usually recommend at least 3 correct repetitions in a row and Mateusz Marcinowski asks what is the significance of 3 rather than like 5, 10, or 20 repetitions?
If we count closely being very strict with ourselves, 3 correct repetitions in a row will most likely mean about 10 total repetitions (sometimes more - even up to 20).
Here's the thing - often we don't notice our mistakes. Often we count only mistakes in notes and rhythms. But what about articulation, what about rhythmical hesitations, what about wrong fingering and pedaling, ornaments, posture, hand, and feet position? These are things that could be improved too.
That's a lot to think about, isn't it?
That's why we have to look deeply at what we are doing, how we are depressing the keys and pedals, how we are sitting etc.
What happens when we play just one or two correct repetitions?
I think that our bodies can't internalize the fragment successfully when we move on to the next fragment too soon. We will have to go back and correct those mistakes later on anyway (if we want to perfect the piece).
So I say we need 3 correct repetitions in a row of the fragment of a hymn or an organ piece but in reality it's more like 10 total repetitions (if the tempo is slow enough and the texture is clear enough).