It's the range. That has been stated somewhere.Everyone can use the basic UWP, but how it is interpreted means everyone will probably see the same thing in a different light. Take world size: 8 = 8000 miles. Depending on how you interpret this: is it EXACTLY 8000 miles, or 7500-8499 miles?
Yes, but the point of having an OTU (as opposed to everybody's personal TUs) is that once someone (someone official, that is) has written up a world and included the exact size, subsequent authors are supposed to stick to that.Unless somewhere in canon it gives the exact same size, people are going to have different interpretations.
And as Robert Prior once wrote: "The very act of writing a Traveller book closes the doors on possibilities. Any game supplement does that, assuming the publisher cares about internal consistency."And once you release your gamers into the OTU, they may impact it in ways that changes that universe; so to paraphrase: no OTU survives contact with players...
Hans