There is no limitation on the period for assessment:

1. If a personal holding company fails to file with its return a schedule regarding its status as a personal holding company.

2. In the case of a deficiency attributable to the application of a carryback (capital loss, net operating loss, or investment credit carryback).

3. If the taxpayer files a false return.

4. If the taxpayer omits from gross income an amount which is in excess of 25 percent of the amount of gross income stated on the return.