"Among the things being announced by NASA was that the launch date for the first SLS mission was being slipped to late 2018 from its current 2017 date. But NASA did not want to call it a slip and said that everyone was still working according the schedule they had been working on. Of course this would mean that NASA has spent the fast few years working toward a date 2018 date while telling the world it was focused on 2017. Later in the telecon NASA said that it might launch the first SLS mission in late 2017 or early 2018. So in other words NASA does not actually have a clear idea when it will launch the first SLS mission. You can be certain that it will slip again - well into 2019 before a first launch date is even discussed. But NASA wants you to know that they have 70% confidence in all of their plans at this point. But when asked what the previous level of confidence was they admitted that they had never done the calculation. So were they more - or less confident prior to this? Given that they just slipped their launch date by a year ..."
NASA Commits to SLS Launch Readiness in November 2018, $7 Billion for Development, Space Policy Online
"Gerstenmaier extolled media participating in the teleconference not to get "hung up on the first launch date. ... NASA has been saying that the second SLS launch, EM-2, which will be the first to carry a crew, would take place in 2021, but today Gerstenmaier said 2021 or 2022. The launch rate thereafter is only once "every couple of years," Lightfoot said."
"But as of today, the only actual missions that are covered by NASA's projected budget are three test flights: the December launch of an uncrewed Orion capsule atop a Delta 4 rocket; the first SLS test flight in 2018; and the first crewed test flight around 2021. While the rockets are considered essential to deep space exploration missions like a proposed asteroid visit and eventual flights to Mars, no such missions are currently funded or even in detailed planning."