KATE?

So I've been curious and have gotten some less-than-helpful answers that really just make me try harder to get to the bottom of this.

Most of you Nerf fans have probably noticed the small letters printed on some of your darts.  On Streamlines, I've found A, E, T, and K.  On Whistlers I've also found K, T as well as J.  K seems to be the most common type I've found in my collection... but I'm wondering what they mean.  Of the Streamlines that I have, the E and K types tend to be the best and most durable... so are they just different manufacturers?

...or does the guy who oversees Streamline production have a girlfriend named Kate?