I am now confused.
I looked in the book, and yes your correct. Table 6-7 dose list Uncommon Martial Weapons.
However, the official online rules, Archives of Nethys, has this for Kukri
Kukri
Source Core Rulebook pg. 281
Price 6 sp; Damage 1d6 S; Bulk L
Hands 1
Category Martial
Group Knife; Traits Agile, Finesse, Trip, Uncommon
The blade of this foot-long knife curves inward and lacks a cross guard at the hilt.
Critical Specialization Effects
Source Core Rulebook pg. 283
Certain feats, class features, weapon runes, and other effects can grant you additional benefits when you make an attack with certain weapons and get a critical success. This is called a critical specialization effect. The exact effect depends on which weapon group your weapon belongs to, as listed below. You can always decide not to add the critical specialization effect of your weapon.
Knife: The target takes 1d6 persistent bleed damage. You gain an item bonus to this bleed damage equal to the weapon’s item bonus to attack rolls.
Also from the Archives of Nethys Base Weapons, (https://2e.aonprd.com/Weapons.aspx), lists Melee weapons category as Unarmed, Simple, Martial, and Advanced. Uncommon is listed as a weapon trait, not a category.
I wonder if this is some kind of error in one of the sources, as the printed book and the official online rules seem to disagree.