40 CFR § 86.404-78 - Section numbering.

(a) The year of initial applicability of a section is indicated by its section number. The two digits following the hyphen designate the first model year for which a section is effective. A section remains effective until superseded.

Example:

Section 86.411–78 applies to 1978 and subsequent model years until it is superseded. If a § 86.411–81 is promulgated it would take effect beginning with 1981; § 86.411–78 would apply to years 1978 through 1980.

(b) A reference to a section without a year designation implies the appropriate model year.

Example:

When considering 1979 vehicles a reference to § 86.411 implies § 86.411–79. However if no § 86.411–79 has been promulgated then § 86.411–78 is implied; See paragraph (a) of this section.