getCoreResults Is the correct method to access the results of a query type parameter in reporting.
Based on the fact that your table is showing as empty in preview, I would say that your tag history query is returning no rows. getRowCount() returning 0 would support with this.
Double check the parameter values being fed to the tag history query. Are you defining valid start/end times to the query? Is there actually data for the time span you are querying? Are you correctly feeding the parameter values to the query?
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