Saving result and compare

How can I save my test results? I want to compare between 2015 and 2016 reports. But I didn’t find the rest report after running my test URL. Example It was one test URL of 2015
But when i run " Test not found" message is shown. How can I get the 2015 result reports?

You might not be able to. There was an issue with the archived tests a year or two ago that resulted in a lot of the old results being deleted.