The Dark Angels, outwardly, complied with the Codex Astartes (which is what split the Legions), but secretly they maintained a Legion structure, such that all of their chapters still fall within a hierarchy and shared command structure (hence why all Dark Angels successors that share the "unforgiven" moniker have Deathwings). More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.