[sjard]

There are plenty of sources that would argue that point. With some pointing out that the first use of the term katana (to differentiate newer swords from the tachi) shows up right at the beginning of the listed time period (1170-1190 somewhere in there).

So as with anything heard on the internet, mileage may vary (including with this post). For most game purposes, use the term that would be most appropriate for your game, and players. Don't worry beyond that.