While they define progression up to level 60, after level 20 Epic BAB progression is used instead (1 every 2 levels). The 60 levels would have been more relevant in pre-expansions since the base game did not have codified epic levels, but NPCs could be given multiple classes and higher than level 20.
|Column||Example Contents||Valid Values||Description and Notes|
The amount of BAB to get at that level based on the row ID column.
Note that since the ID row starts at 0, level 1 of a class would be row 0 (eg: value of 1 for the cls_atk_1.2da file).