This paper describes an extended version of the KoKo corpus (version KoKo4, Dec 2015), a corpus of written German L1 learner texts from three different German-speaking regions in three different countries. The KoKo corpus is richly annotated with learner language features on different linguistic levels such as errors or other linguistic characteristics that are not deficit-oriented, and is enriched with a wide range of metadata. This paper complements a previous publication (Abel et al., 2014a) and reports on new textual metadata and lexical annotations and on the methods adopted for their manual annotation and linguistic analyses. It also briefly introduces some linguistic findings that have been derived from the corpus.