Why the -tic ending for "alphabetic"?

The word alphabet in anniversary is a-l-f according the the abbreviation principle.  The word alphabetic is a-l-f dj a representing the -tic sound at the end.  My question is why if the t is already assumed would the "a" for etic be added and not just a disjoined k?

(by Ryan for group greggshorthand)

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