The victory scores of the pilots represented at List of World War I flying aces (pilots with at least five victories to their credit) often cannot be definitive, but are based on itemized lists that are the best available sources of information. Loss of records (especially records of casualties and lost aircraft, which are at their best a very good guide to the degree of over-claiming), by mischance and the passage of time – and the detail to which such records were kept in the first place – often complicates the reconstruction of the actual count for a given ace. Additionally, the German victory confirmation system began to buckle in February 1918; after August 1918, such records as survived were unit records.