Undated GCM's are generally posthumous. They were issued to sailors who were MIA and later declared KIA. Technically a sailor who enlisted in 1941 and was MIA in 1942 ( and was really KIA in 1942 ) , but was not declared KIA until 1946 would have qualified for a GCM based on 4 years of service !
The Pearl Harbor medal you pictured above will always be scarce because the US Mint made them and they were never sold out the back door like other more recent medals ( including MOH's ) .
If qualification for award of the USN GCM is four years, then I think in this case, the Navy Department awarded it to Pearl Harbor KIA's that didn't actually have their entire four years in? According to Jack Wood's service records, he enlisted on 9/9/38, so he had only 3 years, 2 months and 22 days active duty. Is that unusual or do you know of other cases of early award of the GCM by the Navy?
I know that if a Marine KIA had 3 years, 11 months and 29 days active duty, won the MOH resulting in his death and was an outstanding, professional with perfect 5.0's, his next of kin were SOL if they applied for the GCM on his behalf. It sounds like the Navy had a little leeway?
I've only seen one 50th Anniversary medallion listed on eBay several years ago and if I remember correctly, the seller was asking $200 and I don't believe it sold. When I was doing a work study with the DAV at the local VA hospital here, the medallion had been authorized by Congress and already in circulation for a couple of years and yet, I was totally surprised at the number of Pearl Harbor survivors or next of kin who live in this area that weren't aware of it's existence. It was a well hidden or not very well advertised award for the men and women who were elgible.