Adobe Analytics data discrepancies Month over Month

Hi All,

I am facing issues with changes in the count of some metrics like unique visitors, visits and page views month over month for one of our engagements. 

The count of each metrics noted earlier, for eg: if we take the month of December, the number of unique visitor is 300, visits is 711, page views is 2655, etc  however when i am checking the dashboard now with the same date range(December) the adobe report is showing change in count of unique visitor as 284(earlier it was 300), visits as 689(earlier it was 711), page views is 2651 (earlier it was 2655),etc. Similarly for all previous months its showing change in data.

What may be the reason for this issue? Is there any solution to tackle it? Your responses appreciated.