Final answer:
Multiple code sections can have the same section number, making option b incorrect.
Step-by-step explanation:
The INCORRECT statement regarding the structure of the Internal Revenue Code is option b: 'Each Code section is used only once in the Internal Revenue Code.' This statement is incorrect because multiple code sections can have the same section number. For example, there are multiple sections numbered 24 in the Internal Revenue Code.
Option a is correct. Code section numbers do start over in each chapter. Option c is also correct. Code sections inserted between existing section numbers are indicated by adding a capital letter to the section number.
Furthermore, the Internal Revenue Code is indeed Title 26 of the United States Code, so option d is correct.