This doesn't necessarily help with the ID of Tarev's, but maybe a little on the identity of the cultivar 'Little John'. I contacted the Australian Native Plants Society and this is what they said "It's more related to C.viminalis than C.citrinus but it's probably not a pure form of C.viminalis either. Most references that I've consulted consider it to be of hybrid origin with C.viminalis as one parent. I don't think anyone is really sure of what other species might be involved in the parentage."