Many names that are nicknames or short forms of other names are used independantly.
Nancy,
Eliza,
Jack, and
Joe are but a few examples.
Stacy /
Stacey is no different.
Anastasia is a feminine form of
Anastasius, which means "resurrection". Therefore, if the parents intend for
Stacey /
Stacy to be derived from
Anastasia (which is usually the case in females),
Stacey /
Stacy too would mean "resurrection".
Miranda