Each encounter has two version, A and B. Both version pull from the same pool of there monster types (but it is possible for them to appear unrelated, as they can use disjoint subsets of these three monster types).
In contexts where a single byte (number from 0-255) is used to indicate an encounter (in other words, scripts), the encounter id itself refers to the A encounter, and the counter id plus 128 refers to the B encounter.
Ranges specify the range of numbers of each enemy that the encounter uses. This is specified separately for A and B.
This flag prevents the player from running from the encounter. This is specified separately for A and B.
Music settings 0, 1, and 2 refer to music ids 17, 18, and 19 respectively. 3 is a special setting that doesn't change the music when entering the battle. This is specified separately for A and B.