It is well known if it is understood imperfectly. You will notice that I use the term "nihonto", which literally translates as "Japanese sword". This refers to the general category of Japanese swords, rather than a specific style, such as the katana.
While the more obvious physical characteristics of the nihonto have not changed over many centuries (moderately curved, two and a half hand to two hand / tsuka grip), there were dramatic changes in the purpose and form of use over this period, changing from primary use to foot, to mounted combat, and vice versa.
From fighting lightly armored opponents, then heavily armored samurai, to unarmored fences Changes in forging and changes in access to imported minerals and pre-processed steels of various natures and qualities also changed the nature and quality of the leaves produced.