40 CFR 86.1304 - Section numbering; construction.
(a)Section numbering. The model year of initial applicability is indicated by the section number. The digits following the hyphen designate the first model year for which a section is applicable. The section continues to apply to subsequent model years unless a later model year section is adopted. (Example: § 86.13xx-2004 applies to the 2004 and subsequent model years. If a § 86.13xx-2007 is promulgated it would apply beginning with the 2007 model year; § 86.13xx-2004 would apply to model years 2004 through 2006.)
(b) A section reference without a model year suffix refers to the section applicable for the appropriate model year.