The problem is how the law covering the composition was written. It required the cent to be 95% copper and 5% tin and zinc, but it makes no mention of wha tthe proportions of tin and zinc relative to each other are to be. So a 1941 cent that is 95 % copper 2.5 % tin and 2.5% zinc satisfies the requirements of the law. A 1944 cent that is 95% copper, 4.999% zinc and .001% tin satisfies it as well. Throw a pre 1942 cent into the melt and you have satisfied the 5% tin and zinc spec by providing a trace of tin, But the composition of the 1944 is not really the same as the 1941 even though both meet the legal requirements. For example the 85,590,000 1942 S cents weighing 583,782 pounds were produced using just 50 pounds of tin or .008% tin. The shell case cents used less.