Books and periodicals can shed light on the meaning of the rules and so can loose leaf services that are updated regularly. Today, many commercial sources of information are also available on the Internet, and the primary sources have never been easier to access for free, as they are posted on governmental Web sites. Employers are not required to secure an advance-determination letter. They can take deductions and wait for an IRS audit to determine whether the plan is qualified, but because of the risk of disqualification this is seldom attempted. The item described in the question is a revenue ruling, not a regulation.
Regulations apply to all taxpayers.
Most defined-benefit plans must be covered by PBGC insurance. There is, however, an exception for professional-service employers with 25 or fewer active participants. The qualified-plan rules for Keogh plans and regular corporate plans are similar. Master and prototype plans are easier to use than individually designed plans. Many loose-leaf services are updated weekly.