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You'll find a widget in the Grid's Toolbar that lets you select tables to show in the grid. The selected tables will be stacked together, and Search, Sort, and Filters will then act on that table union. You can also use this mechanism to create "empty" perspectives, by deselecting all the tables from the list. The grid's data refreshes when you click away from the list and the widget closes.
To see which archive records are coming from, click the button and you'll see the first column on the right is a hidden "Source Table" column.
You can treat the column just like any other: sort by it, filter (keep in mind, the Table Selector is the recommended way to filter by Source Table), move it to a different position, etc. You can omit it from Perspectives by hiding it, but this special column will always be available from the Preferences dialog.
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