Using the list as data source mean the chart will auto update when new teams are added. But adding new months will not. Plus adding new months changes the list size and breaks the link with the chart meaning new teams are not added.

Using named ranges will help with the expansion of months but a new named range will be needed each time a team is added.

If you base the chart on a range larger than the current data table you can hide the excess rows and columns and these will be omitted from the chart.
As soon as you unhide a row or colulmn the chart will auto update.
Of course hiding rows/columns presents another problem with regards to makeing user input easy.