Any individual made a member of the Order for gallantry could wear an emblem of two crossed silver oak leaves on the same riband, ribbon or bow as the badge. It could not be awarded posthumously and was effectively replaced in 1974 with the Queen's Gallantry Medal. If recipients of the Order of the British Empire for Gallantry received promotion within the Order, whether for gallantry or otherwise, they continued to wear also the insignia of the lower grade with the oak leaves. However, they only used the post-nominal letters of the higher grade.
Try to answer this question if possible (otherwise reply "unanswerable"): They continued to wear what the insignia of what?
lower grade with the oak leaves