Why does it say that there are 29 cities? There are 38!
Rashi: Shimon took nine of them. 1 (It says (19:1) that they inherited amidst Shimon, and nine of their 13 cities (19:2-6) were among the 38 listed here.)
Malbim: Chazal imply that Kinah v'Dimunah v'Ad'adah (verse 22) are all one; the latter two are outskirts of Kinah. Likewise, Madmanah and Sansanah are outskirts of Tziklag, and are not counted (refer to 15:31:2:3). Therefore, there are 29. 2
Ralbag (36) says that perhaps one of the 15 cities listed below (33-36) did not have a wall, and it is not counted. Perhaps nine of the 38 cities listed here did not have a wall, and are not counted (PF). 3
Radak: We must say that Balah and Besul of Shimon (19:3,4) are not Ba'alah and Kesil (verses 29,30) (even though it seems that they are the same, based on the cities listed before and after them - PF). Malbim - this is difficult. Surely they are the same; pronunciations often change; one who investigates Divrei ha'Yamim knows this! Also Beis Leva'os v'Sharuchen (19:6) are Leva'os v'Shilchim listed here; they are really one city. Also, Rashi must count "v'Chatzur Chadatah u'Kiryas Chetzron Hi Chatzur" (verse 25) as four cities. Chetzron Hi Chatzur implies that they are the same! Also, Chatzur was already counted (verse 23)! Rather, verse 25 does not list anything new; it merely describes Chatzur to distinguish it from Chatzur of Naftoli (19:36). Refer to 15:32:1:2.
I.e. instead of deducting nine cities from Yehudah, Malbim does not count these four outskirts, nor the four that Rashi counts from verse 25, and he counts Leva'os v'Shilchim as one (refer to 15:32:1:1*). (PF)
Bi'ur ha'Gra (18:28) says oppositely, that big cities without a wall are counted, but not listed.