It's fairly simple, even for the pettifogging Polyannas of positivism.
LM is on record at AFA 2014 as predicting 55 DoD orders in 2016 and 41 partner/FMS orders, for a total of 96. The president's budget added two DoN aircraft, for a total of 57. It is my information that long-lead contracts were also awarded for 96.
So the question is whether the 11 aircraft just added will be matched by an increase in production. If not, and the total remains at 96, then the plan relies on 28 partner/FMS orders.
The DoD isn't going to do anything, at this point, that would block sales to partners. So clearly, they don't expect more than 28 orders, which is probably realistic, but someone tipped off Congress to authorize the extras to keep the production ramp in shape.