"I have a person who was an owner at the beginning of the year but not at the end. Should he be on my list?"
No. The list only pertains to those who own the requisite number of shares at the end of the tax year:
List each individual or estate that owns, at the end of the tax year, directly 20% or more, or owns, directly or indirectly, 50% or more, of the total voting power of all classes of the corporation’s stock entitled to vote.