"Same reason we dont count all those little incursions during our wars when we say we havent been invaded in almost 1000 years, they didnt do enough to be considered worthy of breaking the record." That is why history is not only facts but interpretation of fact: The Battle of Lincoln in 1217 is not considered as invasion successfully push back. It is just not considered at all. Or, more recently, 1798 in Ireland, the Battle of Castlebar.