Definitions related to the state of in-progress work adopted in a charter (per § 5.2.6 Working Group and Interest Group Charters):
Adopted Draft is the draft from which the WG will start work. It will usually be the latest document of its shortname in /TR. Once a draft is "Adopted," any changes against it must be resolved through the WG's decision process once the group is chartered.
Reference Draft is "the latest Working Draft published within 90 days of the First Public Working Draft or if no Public Working Draft has been published within 90 days of the First Public Working Draft it is that First Public Working Draft." Systeam is developing a tool by which team can identify the Reference Draft for a /TR document.