I wasn't around when the ZT brand was started, so I can't speak to the original thought process behind the numbering system. However, I can tell you one thing - picking a name for a product is HARD. It's easy to come up with a cool name - coming up with a cool name that isn't already copyrighted is a nightmare. You would be amazed how many beautiful, interesting names have been copyrighted and used on some worthless $2 piece of crap knife. It's one of the more difficult parts of our job.
Ironically, the ZT products tend to be the coolest, so you want to give them some cool, evocative name, but all you get is a number. And, oddly enough, it's a blessing - it takes about five -ten minutes of discussion ot come up with a new ZT model number. Coming up with names for all those new Kershaw knives takes us months - you come up with ideas throughout the year and write them down. Most of those ideas won't make it, so you need lots of them. Funny, but it's true.