I have a copy of Brooker, I., Kleinig, D.(1996) Eucalyptus, An illustrated guide to identification.
Mine is the 1996 edition. It has the right idea, using tree type, bark type, bud count, fruit shape and size, leaf type, colour, location etc.
But I have difficulty using the guide as it expects bud counts to be 1, 3, 7 or >7 and I have a eucalyptus tree with 6 buds as standard.
Maybe a later edition corrects this and might be helpful.