If makers offered promo or starter sets, they were typically the most popular and useful sizes: 3, 5, and 8. Sizes 10 and 12 were also popular. The in-betweens were often not seen as worth spending extra money just to have, e.g. why buy a 4 or 6 when a 5 will do most of the time. So the relatively less-often seen (to different degrees) are the 2, 4, 6, 7, 9, 11, and 13.