Airtable/Excel multiple if statement help (syntax seems the same)

Just started up on Airtable and liking it already.

I'm looking to write some code so that if a cell in one column (e.g. October-19) is within September-November (which it is) the cell with the formula in will show 'Q1 Y2' (our quarters run September-August, don't ask why!).

The problem is I will have to do a huge nested if statement for every month, and then when we get to September-20 the formula will output 'Q1 Y3' and I'll have to run through the next 12 months. Any ideas?

IF({Completion Month}='October-19',"Q1-Y2",
IF({Completion Month}='November-20',"Q1-Y2",
IF({Completion Month}='December-20',"Q2-Y2", etc...

I've tagged this as excel as the if statement syntax seems to be the same.

Thanks, Adam