New data source with backfill data then new data updates

Hello, I have read the article https://community.powerbi.com/t5/Desktop/Adding-in-new-data-to-existing-data/td-p/202312 but I need some clarification.

I am creating a data model and I have historical data from the last 12 months. I will receive the new data in the same format every month. I do not need to refresh the historical data as it will not change. I want to append the new data to the historical to report on historical and new as one data source..

I created a new data source (folder) and it combines all the historical data files. My question comes on what to what to do next? Do I create another data source and filter on the newest file and then load into the model and append to the historical data? Or is there a way to use the existing connection (folder) I created but not load the historical data (But still be able to view the historcial data).

Looking for a best practice on adding new data without having to load the existing data that will not change.

Thanks

Jon