Are the dates correct if you view the Trend Chart in the Analyst? If so it would suggest the problem is Excel's interpretation of the date.
When we view the trend chart in Analyst, the dates are correct.
We reached out to Informatica and they mentioned this is a known bug when we download the scorecard in excel and this should be fixed in future release.
As rightly pointed out, this issue has been marked as a bug and a CR IDE-2549 was raised for this.
This issue is fixed as a part of Informatica 10.2 release. So, please use the latest Informatica product release to resolve the issue.