There is a huge difference between the known plated pattern blanks and purported struck patterns or coins. The mints (plural) did not
need to strike the blanks to know they
could strike coins on those blanks. The mint superintendents, designers, and coiners fully well knew they could strike hard-metal coins and had been doing so for many years. In addition to the U.S. .750 Cu .250 Ni coins (three and five cent), the mints had been striking many hard-metal coins for foreign governments. These included magnetic .999 Ni coins such as the
1928 Ecuador five centavos and
1940 Indochina 10 centimes. Zinc-plated-steel coins were also struck during the war for Allied use in Belgium (the
1944 2 Franc). Chromium steel and stainless steel coins have also been struck by U.S. mints, though later than the war.
The mints sought replacements for the U.S. cent and five cent to
conserve copper and nickel for the war effort, and needed to avoid aluminum and chromium for the same reasons. One explanation for the various blanks is show-and-tell exhibits to get Congress to make a decision ("pick something, anything, just do it now") so the mints could maintain production quotas. Copper use was significantly reduced, but not discontinued, by the mints during the war. In addition to the .100 Cu in the .900 Ag coins, Philadelphia and San Francisco minted .700 Cu .300 Zn coins for Peru throughout the war.
In addition to the eventually used zinc-plated-steel, everything from pressed cardboard (like the OPA tokens) to paper scrip to pressed fiberboard to various plastics was kicked around. Given the rusty shrapnel we constantly see in coffee cans filled with the steel cents, there is a fair argument that they picked one of the worst choices.
That said, there is a huge difference between a
plated coin and a pattern or coin struck on a previously mint-plated blank. Show me a 1943 cent certified by PCGS, NGC, or ANACS
as having been struck on a mint-plated blank, and I'm a believer.