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 4 generations is 59.03% and chances for having a common ancestor in the next 8 generations (between generations 4 and 12) is 97.48 minus 59.03, or 38.45% . Now, with the new information that there were no common ancestors in the last 7 generations, the chance of having a common ancestor between 7 generations ago and 11 generations ago is 75.55%. In other words, this new information not only increased the percentage, but also increased the focusing time from 4-8 generations to 7-11 generations.