What medical histories are you basing your claim that bayonet wounds have been so rare since 1903? If my member serves me correctly, our troops were engaged in two world wars and the (ongoing) Korean Conflict over that time. While the percentage of such wounds is low compared to shrapnel wounds from artillery or bullet wounds, bayonet wounds were not particularly rare in those three wars.
You are apparently also unaware of how records were kept in the days B.C. (before computers). World War II veterans have recently received medals they should have received 60 years ago. If you have a major military installation near you, call the Public Affairs office and ask if there have been any World War II veterans who have finally had their medals catch up with them. Or you can simply look for such stories on line. Such awards are still fairly common here. (In Massachusetts. That's probably because the First Infantry Division was stationed at Fort Devens but spent from February 1942 through August 1945 on a world tour of North Africa, Sicily, Italy, Normandy, northern France and central Germany.)
I would write more on this subject, but I have to attend a funeral for a member of the Big Red One who died Saturday at age 83.
I don't have time to dig through my library so that I can cite page numbers for you but any source will confirm that bayonet wounds are rare, and have been since the Civil War.
A quick internet search found the following paragraph.
The combination of the rifle-musket and minié bullet also made the bayonet nearly obsolete. In earlier years, the bayonet was often the most decisive infantry assault weapon, because the smoothbore flintlock musket's short range allowed attackers to approach close enough for hand-to-hand fighting. In the Civil War, however, firepower almost always decided an assault's outcome before charging troops came within stabbing distance. In fact, very few Civil War surgeons reported bayonet wounds. During Lieutenant General Ulysses S. Grant's bloody campaign against Confederate General Robert E. Lee in the summer of 1864, for example, Union medical directors recorded only 37 bayonet wounds. Of the several hundred thousand wounded men treated in Union hospitals over the course of the war, surgeons noted only 922 bayonet wounds!
You can read it (and more) yourself at http://schools.guilford.k12.nc.us/spages/page/old_PAGE_web/via/sheltonb/Widow.htm
I also recently read something about the 1st Somme and it commented on the rarity of bayonet wounds that were recorded there among the British. It may have been Keegan's Face of Battle but it also could have been in any one of a number of journals or other books.
Now, if bayonet wounds were extrtemely rare in the Civil War, what makes you think they were "not particularily rare" in the mid to late 20th century?