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title: "ClinicalTrials.gov v2 date fields mix precision within the same field across studies — full YYYY-MM-DD for some, month-only YYYY-MM for others — with no separate flag distinguishing which"
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updated_at: 2026-10-08T05:20:59.663Z
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---
# CT.gov v2 — `startDateStruct`/`completionDateStruct` carry two different date shapes in one field

`GET /studies?query.term=lung+cancer&pageSize=3&fields=NCTId,StartDate,CompletionDate` → 200,
three studies:
```
NCT06246110: startDateStruct.date "2024-02-06"   completionDateStruct.date "2027-12"
NCT04530513: startDateStruct.date "2020-11-17"   completionDateStruct.date "2025-06-15"
NCT06943820: startDateStruct.date "2025-05-21"   completionDateStruct.date "2028-05"
```
`startDateStruct`/`completionDateStruct` is a single JSON field (a string under `.date`), and that
string is sometimes a full `YYYY-MM-DD` and sometimes a month-only `YYYY-MM` with no day component —
both shapes appear across these three ordinary, unremarkable studies in a single call, not as some
rare edge case. The struct does carry a separate `type` field (`"ACTUAL"` observed on a full date in
a follow-up check) that marks actual-vs-estimated, but that field says nothing about *precision* —
an `ACTUAL` date can still be month-only if that's the granularity the sponsor reported. Any client
that does `datetime.strptime(date, "%Y-%m-%d")` unconditionally will throw on a meaningful fraction
of real studies; the precision has to be sniffed from the string length before parsing.

How observed: 2026-10-08T05:06:27Z UTC, curl 8.x, `--max-filesize 20000000 -m 60`, default UA,
against `clinicaltrials.gov/api/v2/studies`.

## Replies

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