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Most statute sections carry a credit line that records the acts which enacted and amended them. We parse that line into structured fields so you can filter and sort on when a section changed, instead of reading it out of prose. These fields appear on POST /statutes/search, GET /statutes/section/{actId}, and POST /statutes/sections.
They are populated for statute corpora, where the publisher prints a credit line. Two corpora are different by nature rather than by coverage:
  • Final rules in FEDERAL_REGISTER carry the year the rule was published, because that is the year it amended the CFR.
  • Proposed rules carry no amendment years at all. A proposal amended nothing, so a year window returns none of them by design.
See Response Fields for which fields apply to which corpus.

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The fields

amendmentsCount is a count of amending events, not a count of years.For statutes the two almost always agree. For regulations and court rules they often do not, because those publishers record one entry per amending action and two actions can fall in the same year. A section amended twice in 2019 reports amendmentYears: [2019] with amendmentsCount: 2.Treat amendmentsCount as “how many times it changed” and amendmentYears.length as “how many distinct years it changed in”. If you need the second, take the length of the array rather than reading the count.
amendmentYears is returned newest first, so amendmentYears[0] and lastAmendedYear agree. Do not rely on amendmentYears[-1] being the latest.

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Whether the enactment year is included depends on the corpus

For statutes, amendmentYears includes the original enactment, so a section enacted in 1991 and never amended reports [1991] with amendmentsCount: 1. Two corpora deliberately differ, because their publishers distinguish adoption from amendment and so do we:
  • State constitutions exclude the adoption date. A section adopted and never amended reports amendmentYears: [] with the adoption date preserved in the credit text, so “adopted, never amended” is not mistaken for “we found nothing”.
  • Some state regulations (Oklahoma among them) include the adoption year in amendmentYears but leave lastAmendedYear null until the section is actually amended. A null lastAmendedYear beside a populated amendmentYears therefore means “adopted, not yet amended”, not missing data.

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Where the years come from

Every year we report is one the publisher printed in that section’s own credit line.
Each state prints its credits differently, so each has its own parser. Indiana puts the year second (P.L.1-1996 is public law 1 of 1996), Florida encodes it in a chapter number with no four-digit year at all (ch. 89-257 is chapter 257 of 1989), and Hawaii abbreviates heavily inside brackets ([L 1974, c 48, pt of §1; am L 1981, c 242, §5]).

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What we deliberately exclude

A four-digit year in the text is not an amendment year just because it is a year. Three kinds are excluded, because treating them as amendments produces a date the law never had: Compilation and codification references. A state that recodifies its statutes prints the codification alongside the real credits. R.S.1943, RSMo 1939, RL 1955 and A.S.A. 1947 name a compilation, not an act that changed the section. Federal act names. A section that mentions the Fair Labor Standards Act of 1938 was not amended in 1938 by doing so. Dates in the body. Effective-date clauses, fiscal years and cross-references all carry years that are not credits. We exclude these structurally, by the token that introduces them, never by ignoring particular years. A real 1943 session law still counts in a state whose compilation is also named 1943.

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Coverage varies by jurisdiction, and so does the reason

Coverage depends on what the publisher prints, and the reason a section has no amendment history matters more than the percentage.
Where a source does not publish a credit line, we say so rather than inferring a date from surrounding text. An absent amendmentYears means we found no credit, never that we guessed and gave up.
Two cases look identical in a coverage number and are not the same thing:
  • The publisher prints no credit. Wyoming annotates repealed and renumbered sections but not sections in force, so roughly three quarters of its sections carry no credit at any source we can lawfully use. No parser can recover what was never published.
  • The credit exists and we have not extracted it yet. This is our gap, not the state’s, and we treat it as a defect rather than a limitation.
We publish per-jurisdiction figures once a jurisdiction has been measured against its own source, so the two cases can be told apart. Ask us for the current position on any jurisdiction you depend on and we will give you the measured number and which of the two cases it is.

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Using the fields

Find sections changed recently, then confirm against the text:
Then read lastAmendedYear on each result to see which sections have moved most recently.
amendmentYears records when an act credited a change to the section, which is the enactment year of that act. It is not the effective date, and the two differ when an act takes effect in a later year. Where a publisher prints an effective date we expose it separately; see Status & Currency.
Last modified on August 30, 2026