A lot of the Life pictures are outtakes, and were never published in the magazine.
You're probably right that a good number of the photos that are surfacing now were never published. However, that doesn't mean they didn't publish some things that they could never get away with today.
Case in point, in this Jan 13, 1941 issue, you'll find my personal all-time favorite photo that I've ever found in Life magazine (or just about anywhere else for that matter):
https://books.google.com/books?id=RUoEAAAAMBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Use the page selector on the upper-right to scroll down to page 61. There you'll find the beginning of an article entitled "Democracy in schools". It's supposed to be about "young American's discover the responsibilities of freedom". Yeah, right, whatever. But they have various photos of high school boys and girls. When you get to page 66, you'll probably say out loud: "Oh my"!
That page (66) highlights the "physical training" classes -- high school P.E. in today's lingo. The two photos contrast the girls and boys classes. At the top you see the girls in their gym uniforms doing some kind of floor exercise. In stark contrast to the girls, at the bottom of the page, you see a group of boys. They're not in the gym. They're not exercising. They're not even dressed. There are (by my count) 23 boys, stark naked in the gym showers after class! Their young nude bodies are seen under the water, rinsing off, soaping up and everything else that goes with it. No, you don't see any full frontal shots of the boys -- most are seen from the back or side view showing their tight little bare asses.
No, this photo doesn't have anything to do with examinations, or even anything remotely medical. But ever since I stumbled upon it years ago, I've been fascinated with it. Why did they publish such a photo in a family magazine? How did those boys feel about being seen like that afterward? Why not show the girls nude and in the shower too? What kind of double-standard existed?
Most of all, that photo reminds me of my own high school days in P.E. My high school gym shower was different than the one pictured there, but the whole idea that a large group of boys would be in there together showering was the same for me.