Am I overthinking or will this overwrite the data?

Hi Everyone,

Back to another project for my boss. First I have to give some info then I'll ask my question.

For this one client, my boss pulls two reports, one for internal (excel xlsx file) and one for external (csv file).

The one for internal is not a big concern, as the excel sheet pulls all info from Creation to current date/time. I can easily update Queries from what I know. I'll just filter it to show current month.

The external will only have data that is new from the previous update (daily). How could I append this data to the power query without losing the previous data as that info will technically be gone from its original source (CSV file) but would exist on the worksheet. But as I understand how it works, I will lose all data except for the current day's update.

Is what I am trying to do possible?