why is the autocommand applicable to "line vty 0 4" only? and NOT "line vty 0 15"?
Same goes to Task 8.2 for the rotary feature.
It depends on the version. Some feature sets have more VTYs than others. In any case it always starts at the bottom and counts up. In other words you won't hit VTY 5 unless 0 - 4 are full.