I think St. Patrick as an undocumented migrant is a stretch. Undocumented migrant is a modern, 20th-21st century concept. Patrick's 1st sojourn--6 years--was as a slave brought there from his home in what is present day Wales by Irish pirates. His 2nd and final one was, by his own account, an invitation by way of a dream from the people of Ireland, begging him to return to them.