You choose what's true: they're the same person, she's a different mother, she's family another way (a grandmother, aunt or step-mother, or not related), or you're not sure yet. Choosing "a different mother" or "not sure" keeps both as birth mothers with a red line, ready to put right later. For example, if one record says Grandad's mum is Pat and the other says Rose, you can decide now or leave it for another day.
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