I can only speak for Vietnam as I do not know the figures for other wars:
Vietnam as stated by the govt took place from '65 - '75. In that time there were approx 2.52 Million US soldiers assigned in country and at sea.
Of those, and here the number gets fuzzy some where between 250 - 350 thousand soldiers served in combat. Its not an easy number to count due to how soldiers are assigned, but you can bank on the above numbers a LOT of research went ton coming up with them by the military.
So right off the bat meeting a combat soldier is a RARE occurrence. Meeting a sniper or Forde Recon, Special Forces etc etc is REALLY RARE. I have a lot of stories about meeting supposed heroes and questioning the facts of the story they told.
Allow me to relate one.
I was in Vietnam, been there maybe 9 mos or so and got a letter from the mother of a friend back in the US. The letter was asking me to see her son before he died. She included some of the stuff he wrote and it read like a 'Sgt Rock' dime store novel.
He had regaled his family of incredible feats of heroism, SF, Airborne, LRP, RANGER, you name it and the bullets were flying and he was fighting for his life on a daily basis if not more often. She had included his mailing address and on the next mail run I grabbed the clerk on the chopper that had brought the mail and asked him 'where is this address?' As it turned out it was on LZ English, but a short chopper ride from the LZ we were operating out of. I decided I needed to make a PX run. LZ English was a MAJOR LZ with combined forces, a AF air strip, PX you name it.
I left out a few days later in a lull between going back out again. I arrive and start looking for a running buddy fully expecting him to come repelling out of a chopper with his gun blazing.
I found him, went to the tent were he WORKED, he was the ASSISTANT SUPPLY CLERK. I walk up to his desk and he asks me what I want. I stick out my hand and say JACK. He looks and says who are you? I say, Don...Don who? Don, your running buddy from the real world. He stands up and looks and says I don't know you. Again I say its me, DON, your drinking and running buddy, I drive the white Chevy, you know. He turns white and says "my god, what has happed to you?' JACK, I am out in the bush with the 1st Cav...
Jack has on spit-shined boots, starched fatigues, clean shaved, Army haircut. I have on a flak jacket, no shirt, steep pot, have not saved in days, have not bathed in weeks, tired, hungry and in need of sleep. Jack being the supply guy gives me boots, fatigues, I eat a hot supper and breakfast and leave out the next day on the mail run.
I ask Jack about his letters and he laughs a bit nervously and tells me its for the folks back home, but LZ English is as far forward as he has been in the time he has been there.
Jack is still telling war stories, came across a mutual friend while back and Jack had told him he had made over 10,000 Army Airborne Jumps and had gone to SEALs school to boot.
Sad that Jack has to feel he needs to do this. Jack retired after 20 years, he was an E 6, clearly he did not do well in his career and over the years I came across him on various posts I was stationed on. I would get together with him for a meal, he drank heavy and the more he drank the more he talked of his exploits as a Army super hero. I knew his CO and Jack was a mess up soldier who never saw combat, never did much beyond be a some unit supply clerk...I feel sorry for him mostly and figure he is harmless.