How to read an ISO form number, left to right
Open any commercial policy to the schedule of forms and you get a column of codes like CG 00 01 04 13 or CP 10 30 09 17. Those aren't inventory SKUs — each one is a compact label that tells you the line of business, the kind of form, the specific form, and the exact version. Once you can read the string left to right, a stack of pages turns into something you can actually compare against last year's policy. This is a plain-English primer on the FACTS of the numbering system; it does not reproduce any copyrighted ISO or AAIS form wording.
The part most agents skim past is the last four digits — the edition date. Two policies can list the same form number and still differ in coverage because ISO revised the form between editions. At renewal that trailing date is often the whole ballgame, so this page spends most of its time there.
The four parts of a standard ISO form number
A fully written ISO form number reads as four chunks, left to right: a two-letter prefix, two digits for the form category, two digits for the specific form, then the edition date. Take CG 20 10 04 13 and break it apart:
- Prefix (CG) — the line of business. CG is Commercial General Liability, CP is Commercial Property, CA is Commercial Auto, WC is Workers' Compensation, IL is Interline (forms shared across lines), CU is Commercial Umbrella.
- Category digits (20) — the type of form within that line. On CG, 00 is a coverage form, the 20-series is additional-insured and related grants, the 21-series is commonly exclusions, the 24-series includes waivers and other modifications.
- Sequence digits (10) — the specific form within that category. So CG 20 10 is one particular additional-insured endorsement, distinct from CG 20 37 sitting right next to it in the same 20-series.
- Edition date (04 13) — the version, written month then year. 04 13 means the April 2013 edition. This is the piece that decides whether two identical-looking forms actually match.
Why the edition date is the part that bites
ISO revises forms on a cycle, and a revision can narrow a grant, add an exclusion, or change a definition. Because the base number stays the same across editions, a renewal can carry what looks like the same coverage while a newer edition quietly does less. The additional-insured forms are the textbook example: later editions of CG 20 10 tightened the grant compared with older ones, so a policy moving from an older edition to a newer one can lose ground without a single form being dropped.
The practical rule at renewal is simple: a form is only a true match when both the number AND the edition date match the prior term. An edition change on an otherwise-familiar form is not a match — it's a flag to read the two versions and confirm the coverage still does what the account needs. Reduce the whole schedule to number-plus-edition pairs and the changes stop hiding.
- Same number, same edition — carried forward unchanged; nothing to chase.
- Same number, newer edition — investigate; the revision may narrow or broaden coverage.
- Number present last term, absent this term — a dropped form, the classic silent gap.
- New number this term — added coverage or a new exclusion; read it before assuming which.
Where to find the numbers, and the ones that break the pattern
The form numbers live on the schedule (or table) of forms and endorsements, usually near the front of each coverage part, and again stamped on each endorsement page itself. Read the schedule as your index, then confirm against the actual endorsement pages — the schedule can lag what's physically attached. A few things won't fit the tidy four-chunk model: state-specific and workers' comp forms (WC numbers run longer and carry state codes), interline IL forms that apply across coverage parts, and AAIS forms, which use their own numbering but follow the same logic of prefix, number, and edition date.
The ones to slow down on are manuscript endorsements — carrier-drafted, non-standard forms that don't map to an ISO number at all. They may reference an ISO form or replace one, and their wording is the carrier's own. These can't be read by pattern-matching a number; they need a human to interpret, and a disciplined renewal check flags them for exactly that rather than assuming they're equivalent to the standard form they resemble.
Turning form numbers into a renewal check
Reading a single number is quick. Doing it across an entire renewal — lining every form and edition on the new policy against the prior term, catching the one form that dropped and the two editions that changed — is the slow, error-prone part, and it's where E&O exposure lives. BindCheck automates that diff: it reads both schedules, compares them by number and edition date, and returns a checklist of every form added, dropped, or edition-changed, each finding cited to its source page. It records form facts only — number, edition, and a short plain-English purpose — never the copyrighted form text, and it routes manuscript endorsements to a human instead of guessing. Your first renewal check is free — no card, no demo call.
Frequently asked questions
What do the middle digits in an ISO form number mean?
The two digits after the prefix are the form category, and the next two identify the specific form. On CG, for example, 00 is a coverage form and the 20-series is additional-insured endorsements — so CG 20 10 is a specific additional-insured form. The category tells you what kind of thing it is; the sequence digits pin down which one.
How do I read the edition date, and why does it matter?
The last four digits are month then year, so CG 00 01 04 13 is the April 2013 edition. It matters because ISO revises forms over time, and a newer edition can narrow or broaden coverage while keeping the same base number. At renewal a form only truly matches the prior term when both the number and the edition date match.
What if a form doesn't follow this pattern?
Workers' comp and state-specific forms carry longer numbers and state codes, interline IL forms apply across coverage parts, and AAIS uses its own numbering — but all follow the same prefix-number-edition logic. Manuscript endorsements are the exception: they're carrier-drafted and non-standard, so they can't be read by number and should be flagged for a human to interpret.
Diff your first renewal free — upload the prior policy and the renewal, and see what changed in about a minute. No signup wall, no demo call.