There are differences between the two sets of dates. This is because of new discoveries, and a better understanding of what is already known. For example, in Breasted's 1906 list, he added a ruler in the Twentieth dynasty that further research showed did not exist. Using Manetho writings, Breasted also believed each new dynasty followed the old one in a sequence. Now we know that several dynasties existed at the same time. These changes have changed the chronology by 400 years at the beginning of Dynasty I.