Well normally FO gets 1 70lb bag domestically (2 70lb if you have a DL credit card) and 2 50lb int'l.

I think you can make a case here that since the allowance on your first leg is currently 3 70lb bags, you should be able to check that many through. However it's not clear what the actual policy is.

I know domestically, whenever ANY of my legs have been upgraded, I've gotten the F/J bag allowance.