General Budget Amount Doubt

Hi All,

This is just a doubt which I want to get clarified.

Suppose there is one account which has budget of $100 in MAY-16 and in JUN-16 we have raised PO for 50$ and then we have remaining 50$ left for which we raise another PO for 50 $ in JUL-16.So in JuL-16 the funds remaining is $0 in the account.

Is there any way if we can backtrack and raise a PO with Date in  JUN-16 as it has 50$ remaining funds ??

Note: PO periods are not closed.

Apologize if this is a stupid question.