The 2018 deadline is for substances in the lowest tonnage band: 1-100t. A first step of for companies to decide which substances they will register and join the specific SIEF (Substance Information Exchange Forum). Some 70,000 registrations are expected to be submitted by 2018, for around 25,000 substances, many more than in 2010 or 2013.
http://echa.europa.eu/view-article/-/journal_content/title/reach-2018-find-your-co-registran-1
2018 REACH target looms – ECHA pushes registrants to join SIEFs