The fill style is defined in the first byte. The values are defined below. Depending on that value, the fill style structure changes as shown below. swf_fill_style is a union of all the other structures.
Notice that types 0x42 and 0x43 are only available since version 7 and type 0x13 is only available since version 8.
Note that these values were introduced in Flash 7 but it looks like only player 8 supported the distinction between hard edges and smooth edges on a per shape basis. That would explain why I could not see any difference between smooth and hard shapes when I tested this feature in Flash 7.
Before Flash 8, all shapes would be smoothed if the global quality of the movie was set to BEST. In Flash 8, nothing is smoothed by default whatever the quality and the smoothed or hard selection in a shape can be used as a hint on a per shape basis. Following this specification closely can be important in some situations.