The gaps in the ages of longest-living dogs are quite large, however: the second-oldest dog is in turn almost two years older than the third, there's four years

The gaps in the ages of longest-living dogs are quite large, however: the second-oldest dog is in turn almost two years older than the third, there's four years between #4 and #7 (with the exact gaps between #4-#7 unclear, but there should be at least two gaps of >1 year). This strongly suggests the gap can be attributed to sparsity of data. The gap between Calment and #2 is over 2.5x the next largest gap in the records (1 year 80 days between #4 and #5).