In different versions of the "Masterplan", different explanations were presented to deal with this: according to writer Lance Parkin, in the "original" version of the Masterplan, the Doctor rescued Susan as an infant from Gallifrey's recent past.
Clapham started out writing Doctor Who fan fiction and, through Seventh Door Fanzines, began to work with Lance Parkin.
This means that whilst Wallace's novel Fear Itself was the last book to feature the Eighth Doctor, it is set at an earlier point in the Doctor's life than Lance Parkin's The Gallifrey Chronicles, which is the last Eighth Doctor Adventure.
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