There's another relevant bit in the "inter-available" routes part of the London section of The Manual:
Subject to tickets being valid between the appropriate stations or for the zones shown, National Rail singles and returns only (not Season Tickets) are valid on LU /DLR services as shown below:
National Rail tickets which include validity between Seven Sisters / Tottenham Hale/ Walthamstow Central and Zone U1 or beyond are also valid on LU / DLR services via the Victoria Line from Seven Sisters / Tottenham Hale/ Walthamstow Central to any station in Zones 1 to 3