Updated March 15, 2017
This article explains why old data can be shown in monitored instances in DPA.
This data is stored indefinitely until it reaches that threshold of the clean days of detail.
All DPA versions
Data will be stored up to the defined value for each instance. If you stop monitoring before this threshold is reached, the data remains, and then continues to be stored until it passes the threshold. The cleaner service removes anything older than the defined value.
Example: It is currently March, and you monitored an instance for 10 days total in January. If I start monitoring the same instance now, it still has that data from January for 20 more days. It is not based on the current timestamp, but each date time is a value that we can store up to 30 days of (based on default CLEAN_DAYS_OF_DETAIL value).