Most of the medals I research and return were awarded for service during WWI. This is due to the volume that were awarded and the time since the end of WWI which increases the opportunity for the medals to become lost. I have also discovered that many medals were disposed of during The Depression for their scrap value.
The next largest group of medals I come across were awarded for service during WWII. A few medals from other conflicts also come my way. The oldest I've returned was a Queens South Africa Medal for service in the Boer War, the newest was an Australian Active Service Medal for service in East Timor.
I have also returned several medals awarded for the Vietnam War. In the last couple of days we, mainly through Bill's efforts, have located a Vietnam War veteran whose South Vietnam medal I've had for a few years. The medal has had a hard life since it was lost and I had to remove a fair bit of gunge off the reverse just to see the details. The ribbon is also very soiled. The good news is that the medal will soon be sent back to the veteran. I thought that you might be interested in seeing some pictures of this medal.