User blog comment:Dettles/Doflamingo's Past/@comment-5729687-20130330035518/@comment-5962458-20130330102414

I think you got some facts wrong about the timing.

Z's arm was cut off about 10 years before current events by an unknown pirate.By that time however doflamingo was already a sichibukai since we know that he holds that position for about a decade.Now, that unknown pirate became a sichibukai just 1 year before the current events, which led Z to leave the Navy and form the Neo Marines.

Source: "One year ago, the same pirate who severed Zephyr's arm became a Shichibukai, prompting the instructor and former Admiral to renounce the Marines in order to create his own group, the Neo Marines."