The Form 990 instructions state that for purposes of Item F at the heading of the Form 990, the “principal officer” is the person who “regardless of title, has ultimate responsibility for implementing the decisions of the organization's governing body, or for supervising the management, administration, or operation of the organization.” Application of this definition will vary depending on the organization, and this will not necessarily be the same officer who signs the Form 990 at the bottom of page 1.

Tax-exempt, nonprofit organizations are required by law to file Forms 990 that are complete and correct, but there is no affirmative legal duty to file an amended Form 990 to correct a newly discovered error or omission. While an organization may wish to file an amended Form 990 to manage public perception, show transparency, or mitigate the risk of penalties, this step may not be worth the cost and effort in the case of an inadvertent good-faith mistake like the omission of a single, volunteer Board member.

The IRS instructions for Part VII, Section A of the Form 990 provide that any director or trustee who “served at any time during the organization's tax year” is reported as a “current” director or trustee. In other words, Board members who step down in the middle of the year must appear on the list of directors, officers, key employees, and other individuals reported in Part VII, Section A of the Form 990.