Gas Giants and Belts, p. 427, probability difference
On p. 427, Gas Giants and Belts, 2nd para., it gives the number of gas giants in the entire stellar hex as 2D/2 -2 (ignore fractions and treat less-than-zero as zero).
Since a roll of 6 or more on 2D will give at least one gas giant, this gives a probability of 26/36. However, this contradicts the long-standing principle in past TRAVELLER editions, and in this edition p. 421, that you have at least one gas-giant in the system (hex) on a throw of 9 or less on 2D (probability 30/36).
One possible correction is to round fractions UP instead of ignoring them. Another possible way is to use the formula (2D-3)/2, ignore fractions. This would produce a greater number of gas-giants overall, but rolls of 5 or more would produce at least one, so the probability will harmonize at 30/36.