FYI, back in October 2016, I emailed IWI about the serial number flavors trying to find the birthday of my X95. This is part of a conversation I had with a customer rep:
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Again, we're only the guys that import and assemble these weapons. We have no say in serial assignments. When I was working with our gunsmith, he was explaining the "different flavors" you guys caught on, and there's no significant rhyme or reason for one, or the other, or the other. The T9xxxxxx serials came and went, and the T0xxxxxx guns are being built currently. As far as what they designate: Maybe a higher-up in Israel understands the differences. Or maybe they had three different guys in charge at three different times.
I like cars and I like guns, and in both of these industries you'll find idiosyncrasies that are insignificant to designers, but that drive faithful masses crazy (read: Ford Motor Company). I think it's safe to say that this is the case with the Tavor serialization system. I hope this helps out with your guys' consternation, even though I'm sure it won't. Have a good day, and keep shooting!
Sincerely,
Colin Martin
Customer Service