The Review of United States Human Space Flight Plans Committee, better known as the HSF Committee, Augustine Commission, or Augustine Committee, was a group convened by NASA at the request of the Office of Science and Technology Policy (OSTP), to review the nation's human spaceflight plans to ensure "a vigorous and sustainable path to achieving its boldest aspirations in space." The review was announced by the OSTP on May 7, 2009. It covered human spaceflight options after the time NASA had planned to retire the Space Shuttle. A summary report was provided to the OSTP Director John Holdren, White House Office of Science and Technology Policy (OSTP), and NASA Administrator on September 8, 2009. The estimated cost associated with the review was expected to be US$3 million. The committee was scheduled to be active for 180 days; the report was released on October 22, 2009.
https://www.nasa.gov/wp-content/uploads/2015/01/617036main_396093main_HSF_Cmte_FinalReport.pdf
excerpt p.101
Radiation effects on humans:
Beyond the shielding influence of the Earth’s magnetic field and atmosphere, ionized atoms that have been accelerated to extremely high speeds in interstellar space fill the solar system. The effects of such galactic cosmic radiation on crews on long-duration space flight far from the Earth are a significant concern. Additionally, normal solar flare activity also occasionally releases radiation potentially injurious to humans.
On the Moon or on the surface of Mars, techniques are available to shield a human habitat from these sources of radiation, but the massive shielding is cost-prohibitive for a spacecraft.
These radiation effects are insufficiently understood and remain a major physiological and engineering uncertainty in any human exploration program beyond low-Earth orbit. A 2008 report by the National Research Council concluded, “Lack of knowledge about the biological effects of and responses to space radiation is the single most important factor limiting the prediction of radiation risk associated with human space exploration.” A robust research program in radiobiology is essential for human exploration. Research on these radiation effects on humans is limited on the ISS, since it is partly shielded by the Earth’s magnetic field.
It is clearly stated that, in 2009 the effects of space radiation - beyond low earth orbit - was unknown. So it couldn't have been known for any of the Apollo missions.
That’s why they each carried radiation dosimeters, to record their exposure. While it is true shielding completely would be impossible or impractical, that doesn’t mean it will kill them. According to a transcript I heard, the medical people informed one of the flights they had received (at that point) the equivalent maximum daily radiation exposure of someone working in the nuclear industry. The Van Allen belt is not a place you want to hang around in, but it won’t kill you. In fact near as I can tell all of the flown Astronauts are pretty hardy stock and usually lived to a ripe old age. Jim Irwin was the first to pass, and from cancer iirc. Pete Conrad was killed in a motorcycle accident. But for the most part very healthy and sharp. Buzz Aldrin for example is still extant, and working on his 3rd wife.