^^^ Sorry, LegoLord, but there is no historical evidence for swords cutting through plate armor. What you're referring to is using a sword to bash through subtantially weaker metal, which was not advised by any of the fight manuals we've got today, because plate armor was generally made to withstand a lot of force, was much thicker than a sword, and was made of the same quality materials.
The way to use a sword against plate armor was to grab its midsection for greater point control, and to stab at the weaker areas of the armor, such as vulnerable joints, or to reverse it entirely and use the hilt as a warhammer.
For further evidence, please remember that plate armor was made to withstand piercing attacks, which are like slicing attacks only with a lot more force over a much smaller area. If this was the case, then you'd need an extraordinary slash to cut through something so designed.
I'd like to provide you with some sources, but all I have is the ARMA website which I despise, yet accept as a necessary evil.
However! Societies which lacked much metal (Read: most oriental civs, most famously Japan) would have to come up with armor which worked without metal. As such, these armors were generally inferior to their swords, which made for the nifty cut-you-in-half legends we see today.