The statement that shirk is unforgiven must not be applied indiscriminately to anyone who has ever committed it. A former idolater who turns away from shirk and believes is not in the same theological situation as a person who dies persisting in it.
Example 1: A person previously committed shirk, then repented and entered Islam; the condition of dying upon shirk is absent.
Example 2: A person dies still adhering to shirk; that is the case addressed by the exclusion of forgiveness.
The question concerns the final state of faith and repentance, not merely a label attached to someone's earlier life.