How is the other plugin collecting the data? is it using google analytics?
Our plugin saves the data in database and only pageviews since the plugin was installed is collected. But it does collect information on new and old post. You will have to change the date display limit to display older post in the widget.
If you had another plugin collecting data in the database using the post metadata, there is a setting in the widget to change the value. You will have to know what was the old post metadata key