A:
Normally, a resignation is voted on (and should almost always be accepted) at the first meeting at which the resignation is announced.
If it was not voted on then and a reasonable time has elapsed during which it could have been accepted, it may be assumed to have been accepted.
(RONR p. 292.)
It would seem that a reasonable time has passed, so we may infer that the office became vacant in July, and that the resigned Chief is now unofficially acting in the role.
It's likely your bylaws direct you on how to fill the vacancy.
If they give no direction, you should give notice of election, then elect the new Chief.
The minutes should accurately reflect what took place during each meeting.
If it's what occured, then the minutes of the March meeting should say that the Chief announced his resignation effective in July.