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"Katherine matching Kate" probably refers to him listening to the recordings where some people say Kate instead of Katherine.
Which recordings do you mean? Doing a search for "find Kate" only gives this one
The recordings of the dead people that the agent is transcribing for us. He mentions in some places that he has trouble hearing exactly what they are saying or what spelling to use, like he does in 20-DI-1 for Kate/Catherine/Katherine.
