There is no need to enter the code BP 2016 Form 1099-R on your 2015 tax return either now or as an amendment, although there is no harm in entering it now. Doing so will have absolutely no effect on the tax return. (Try it and see. The amount in box 1 will be the amount of the excess distributed (adjusted for loss), box 2a will be zero. You'll see no effect on any part of your tax return including Form 1040 lines 7 and 16.)
