I agree with the other post, I think the medals are very new, definately post-Vietnam. I know that many Vietnam MIA medals, at least to aircrew, were commonly awarded in the mid 1970's, like 1975 and 1976, when the Defense Department finally changed the status of most Vietnam MIA's from missing to dead / killed in action. That happening sometimes triggered the issuance of posthumous medals to the survivors of those who had been listed as MIA but had just had a status change to KIA. So... finding mid-1970's period medals to Vietnam MIA's is not uncommon at all. However, I think yours are much newer then that - probably no more than 10 years old or so?? They just seem to have a sheen or shine or finish to them which makes me think they are just not that old. In addition, yours have had the broaches / pins removed. That does nothing really to date them. It does tell me that they were probably at one time mounted in a frame perhaps??? I would have expected a Purple Heart to be in the group too. Although the information you put in the post does not appear to show they were all killed in action as opposed to having crashed from a lost engine or something, since at least at face value the reason for their loss was unknown, I would have expected a Purple Heart to have been awarded too. The apeparance that these medals may have been removed from a frame would lead me to speculate that there might also be other medals, like a Purple Heart, floating around out there somewhere too. Tough to say for sure though.
Just as an aside, Vietnam MIA groups can at times be difficult to research. Because of the shams and scams out there related to people contacing Vietnam MIA families and trying to get money from them for search efforts, because of "sightings", etc, the Defense Department really clamped down on public access to records of MIA's. So, with that said, you may find it hard to get his service records.
Ultimately though, the thing you need to do is to request his service records and see if you can verify these awards in Adam's service records, see if he got the Air Force Commendation Medal and Vietname Campaign with one star, etc.