In this book, Abbot Mortimer said to Matthias that Martin the Warrior came to Redwall when its founders were under attack by a "great wildcat." Apparently, he almost died, but was taken into the Abbey, where they "cared for his hurts." Here's where the mistake comes in: Redwall didn't exist when the war took place!
Actually, Martin and co. founded Redwall with Abbess Germaine after they left Loamhedge Abbey (found and described in Mattimeo). Did they mention in context that it was, indeed, Redwall they were talking about or did it just say 'abbey?'