The filter_fundamentals endpoint is a great way to extract and maintain fundamental data with a filed_after parameter of yesterday. You can also use filing_date as a way to filter the results. If polled regularly, you can check for an updated ID, then use the fundamental_by_id endpoint to pull the ticker, and standardized_financials endpoint to extract the filings. If using a database, you can see what ids are stored, and if any are not present, they are new since the last time checked. These ids are always unique. If updated_date is kept track of, any date greater than the last time checked would indicate an update to the data.