## The problem
Using the Dust upsert-document API (POST /api/v1/w/{wId}/spaces/{spaceId}/data_sources/{dsId}/documents/{documentId}), passing a negative Unix timestamp for document dates before 1970 (e.g. -106245523000 for August 1966) blew up with a 500. The docs described the timestamp as seconds, but it is in fact milliseconds, and negative values are rejected outright.
## What fixed it
Negative (pre-1970) timestamps are not supported: the backend parses the timestamp field as an unsigned 64-bit integer, so a negative value 500s, and Dust's team decided not to add support. The unit is milliseconds, not seconds as old docs stated. Workaround from the thread: don't rely on the timestamp field — put human-readable dates at the top of the document text (e.g. `$createdAt: 1966-08-20`), which retrieval does match, and for hard date filters use document labels/tags with the in-conversation tag-filtering feature instead.