The ruling on one who shaves his head but does not cover all of his hair in Hajj or 'Umrah

May Allah reward you, O honorable Shaykh! A man performed 'Umrah or Hajj, and when it came to shaving, he did not cover all of his hair. A number of years have passed since his pilgrimage. What is the ruling in this case? We also want a general rule: when a pilgrim or one performing 'Umrah leaves something of his own [obligations], when do we order him to return to Makkah and bring it [to completion]?
This is leaving an obligatory act, and leaving an obligatory act requires a fidyah, which is slaughtered in Makkah and distributed to the poor. With this, his Hajj is completed. As for what is required of the pilgrim to do if he leaves it, those are the pillars. As for the obligatory acts, if their time passes, they are made up with a sacrificial animal.