Tagging columns

Hi All,

Hoping to get some insight on the following. 

I have two tables:

1. First table stores historical data (snapshot of each month for full fiscal year)
2. Second table stores data as at the current month (i.e. contains data for full fiscal year but the forecasted sales and actuals are all depicting the figures as of this month (i.e. Oct).

I want to create a tag against Table 2 that basically tags every row as 'Oct-21'. Then when we move into Novemeber, I want the tag to automatically change to 'Nov-21'. In this way, when i select Oct-21 slicer, i get a full YTD view as well as an accurate forecast of what sales looked like at this point in time. Without this tag, when i click Oct-21 slicer, it just shows me oct figures. 

So the table should look like this (addition of 'FY' column)