Because your rows are in the order you want your chart, you can simply handle this by turning on the "Row Order Levels" Column Property for your "Year/Mo" column.
To do this, move your cursor to the column header for the "Year/Month" column. Right click and select
Column Properties==> Row Order Levels.
The order of the axis for any charts you make for that column, will then be in the order the data are in the data table.
Jim