Mahou Shoujo Lyrical Nanoha StrikerS THE COMICS

Chapters 1-3 are the events that occurred between the end of A's and the start of StrikerS.
Chapters 4-12 are side stories about the characters.
Chapters 13 & 14 are the events that occurred after the end of StrikerS.
Chapter 15 is a special from Megami September 2009 (also events after the end of StrikerS).