Could it be that they didn't understand what was going on at the time and there's no extant proof one way or the other?
If the blight took out the plants that were most susceptible and the plants that survived were ones that had slightly mutated to produce better blight resistance, or the blight itself mutated to become less infectious, I suppose that might not be apparent to the people doing the growing. To them the blight may have just 'got better' even though they didn't do anything obvious different?
They must have had resistant stock of some sort: you can't grow new potatoes by taking slips from a blighted potato, so whatever they grew from by year 3 must have been either from outside, or was descended from the more resistant plants.
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If the blight took out the plants that were most susceptible and the plants that survived were ones that had slightly mutated to produce better blight resistance, or the blight itself mutated to become less infectious, I suppose that might not be apparent to the people doing the growing. To them the blight may have just 'got better' even though they didn't do anything obvious different?
They must have had resistant stock of some sort: you can't grow new potatoes by taking slips from a blighted potato, so whatever they grew from by year 3 must have been either from outside, or was descended from the more resistant plants.