Progress within a band is hard to define. You could determine that progress is more technically driven, songs where the progress would be that  the members have become more masterful with their respective instruments. Perhaps you could define progress through being more daring and forward thinking in their approach, trying new sounds and different ideas. Or you could define that progress is when a band is truly cohesive, when not just one particular area of the band excels but the unit as a whole is immovable.