Combine monthly files with Power Query, using an LLM one step at a time

Create a folder that holds only the files you want stacked. Microsoft's guidance is to keep them in "a dedicated folder without extraneous files", each with the same column headers, data types and number of columns. Column order doesn't matter because columns are matched by name.

Select the folder, then choose Transform Data so the Power Query Editor opens with the list of files. Filter the Extension or Folder Path column so only the files you want remain.

Select the Content column, then Home → Combine Files. Power Query uses the first file as the example; pick a different sample file from the drop-down if the first one is unusual. Only tick Skip files with errors if you will check which files were skipped.

For anything the ribbon can't do easily, describe one change and paste the current query from Advanced Editor. The r/excel user who works this way: "it's best to break the project into small pieces" because "the more complicated my instructions are, the less likely ChatGPT 4 is to get them right. Therefore, I break down the project into steps and test each step along the way."

Paste the result back into Advanced Editor, click the new step in Applied Steps, and check the preview's row count and columns. Another r/excel user who has Copilot define M steps warns: "It makes mistakes, though, so you have to check it and fill the gaps anyway."

Select Close & Load. Next month, drop the new file into the same folder and refresh; Microsoft's walkthrough describes setting it up once and then refreshing to see each month's results.