Hmmm. Agnes was really killed during the episode, and as you say it was maybe a few weeks or less, but it was still part of the episode and was investigated first off. In Judgement Day, Mrs. Foster was the first victim of Bella Devere (as Annabel). Even though it was way before the main events of the episode, the murder was intertwined with the plot, even though it was at the end. The murder of Agnes shouldn't be considered "Prior to the Episode", but the murder of Mrs. Foster should, but it still should be listed in the murder tally.
So now, what about Gaius Quintus in Death in Disguise? And "12 Deaths of The First World War" in Four Funerals and a Wedding? I don't think that they should count in the murder tally. They are just listed for information.
Do we need to annotate the murders that are not to be included in the tally?