This is probably not true, fwiw. People telling the truth will have minor variations in their story each time they tell it. Telling the exact same story each time is literally one of the signs a lot of prosecutors look for to tell if someone is lying. It's a hint that someone is recounting a carefully memorized story instead of a real memory. Our actual memories are not photographic and tend to change and vary a bit over time. One of the interesting things studies have found is that
the more often a memory is recalled and retold, the less accurate it becomes. Something about the process of remembering and retelling appears to make the memory malleable for a time. I think the theory is that the actual act of remembering puts the synapses into a more volatile state and that makes the memories more susceptible to modification, but I'm not a neuroscientist so take that with a grain of salt.
I think it's very valid to look for major inconsistencies or changes in a story. Like if Don said he was at work all day and it turns out he was actually at home. But personally, I think the variation between walked halfway to the house, vs walked to the porch, vs walked to the door is pretty minor and probably falls well within the variation you'd expect from multiple retellings.