Politics often causes acts of bravery to be overlooked. Sometimes they don't want to admit to battles that cause what are considered heavy casualties. Also, sometimes commanders or staff, too far removed from actual fighting, don't know, or have forgotten what bravery is. There was a 173rd Abn battalion commander who refused to forward a recommendation for a bravery award. The soldier had fallen on a grenade to save his comrades. The battalion commander said he wouldn't recommend a bravery award for someone who committed suicide (?). Others kept pushing and the soldier was finally recognized with the award. Sometimes those who witness bravery are themselves killed; no witnesses. Those kinds of things happen, sadly. But often I think, it is that some battles end up having so many acts of extreme bravery, it is hard to single out individual acts. They are just part of the norm. Plus, a lot of soldiers don't seek medals. They are more interested in survival.
When I got to Vietnam in late 1967, the Aussies were still spoken of with great respect within the 173rd Abn Bde, although they had been detached. Those who served with the 173rd were invited to be members of the 173rd Association. Good solid troops!