A determination letter is a start, not a shield. An organization that fails to file its Form 990 series return for three consecutive years loses its exemption automatically under section 6033(j), with no notice of deficiency and no appeal, and the IRS publishes the list.
Status also turns on arithmetic. A public charity must draw at least one third of its support from the public over a rolling five-year period or pass a ten percent facts-and-circumstances test; fail both for two consecutive years and it becomes a private foundation, with a tax on investment income, a five percent annual payout and a self-dealing regime that reaches ordinary dealings with its own board. A director who sells property to the foundation owes an excise tax on the amount involved even if the price was fair.
We form the entity for the classification it will actually hold, draft the compensation procedures that earn the rebuttable presumption of reasonableness under section 4958, and read the Form 990 before it is filed, because the examiner reads it afterward. When the matter is before the IRS, we represent the organization in it.