In the mid 90's,the Next Generation(model 1221) was introduced.
The serrations were put on the left side as it looked better with the Ka-Bar logo.
Some years later,not sure how many,the serrations were moved to the right side as most people are right handed,they cut better.
I've used both styles,but prefer the right side variation myself.
Thats my understanding of it anyway,and I may be wrong.