Chapter numbers shall be spaced to allow for expansion and a minimum of one number shall be omitted between chapters of a new or revised part, subpart, article, division or subdivision. Where related sections are grouped under a heading within a chapter as provided for in §§ 9.14-9.16 (relating to chapters, subchapters and undesignated center heads), numbers shall be reserved at the end of a group to allow for expansion.
1 Pa. Code § 9.37