New GI Bill

Can anyone explain the new changes to the Post 9-11 GI bill. For example the additional 12 months if you opted out of the MGIB to use the Post 9-11 GI bill.

If I am reading it correctly, since I opted out of the MGIB to use the Post 9-11 GIB, I can either recoup the $1200 or add an additional 12 months to my already 36 months equally 48 months of Post 9-11 GI bill??

Please break it down Barney style, TIA!