When you first start using Moz Analytics, it's important to remember that the data on the historical charts is subject to change. The "Metrics Over Time" chart is designed to show rank changes over time. Therefore, you should make sure that your historical data is the same. If you have a Moz Pro account, you can view old DA information for a limited time and export it for analysis. You can also save snapshots if you want to compare the data over the years.