Maxio's preview tables (ie. preview_line_item, preview_performa_invoice) contain data about incoming things (invoices, subscriptions etc.) these items eventually get issued and are shown where they belong (ie. upcoming invoices move to the invoices table when they are issued but are not deleted from the preview table.) I have opened a ticket with Maxio to better understand this and they confirmed that once an item is "issued" it doesn't belong in the preview table anymore. currently the issue with these tables is that they contain a large number of duplicates and expired data. 

the duplicates are coming from changes to the invoice, meaning if a customer plans to increase their services for the upcoming period instead of editing the existing preview invoice it just creates a new one without indicating that the old one is out out of date. 

meanwhile the _fivetran_deleted column is set to false. a solution to both of these issues would be to update the deleted column to show the right value. 

thanks.