Ethnologue (206) treats all but Ngumbarl as distinct languages, and this view is supported by those linguists who have worked on the languages, including Claire Bowern and William McGregor.
There is considerable documentation of the Bardi language, but most of it is unpublished. The earliest work on the language dates from the 1880s, although that has been lost. The earliest records are from the very early 20th century. Gerhardt Laves spent some time on Sunday island in the late 1920s and recorded extensive textual materials, and steady documentation has progressed since the late 1960s.