These are cumulative probabilities. That is the key to understanding something that initially seems counter intuitive.

Let’s use an example for a specific situation of one mismatch in 37 markers. Before inputting your information, the chance of having a common ancestor in the first four generations is 59.03% and chances for having a common ancestor in the next eight generations (between generations four and twelve) is 97.48 minus 59.03 or 38.45% . Now, with the new information that there were no common ancestors in the last seven generations, the chance of having a common ancestor between seven generations ago and eleven generations ago is 75.55%. In other words, this new information not only increased the percentage, but also increased the focusing time from four to eight generations to seven to eleven generations.