A resource map can only be 32K, and it contains all of the resource names. Resource names are used to store the user visible configuration names. Each entry has a little overhead so the average name length, plus a little overhead, times the number of configurations, must be less than 32K.
If we assume 30 character names, and 10 bytes of overhead, then the limit is 32K / ( 30 + 10 ) = 819.2 configurations. Resource names can be as long as 255 characters, so worst case is 32K / ( 256 + 10 ) = 123.2 configurations.
Note: Apple recommends not saving more than 120 configurations with ARA 3.0.