Bates Numbers in Load Files: DAT, OPT, and Review Platform Imports

What a Load File Actually Carries

Stamping Bates numbers onto a PDF is only half the job when the output is headed into a document review platform. The platform needs to know, for every document, what its Bates range is, what metadata fields apply, and where the underlying page images live on disk. That information travels separately from the PDF itself, in one or more load files.

Two formats dominate the litigation support world: the Concordance-style DAT file for document-level metadata, and the Opticon OPT file for page-level image data. A production is rarely considered complete until both are generated correctly and the review platform confirms a clean import with no orphaned pages or unmatched Bates ranges.

BEGBATES, ENDBATES, and BEGATTACH in a DAT File

A DAT file is a delimited text file, one row per document, with fields separated by a non-printing delimiter (commonly a pilcrow, ¶) rather than a comma, to avoid collisions with commas that appear inside normal text fields. Every row typically includes at minimum BEGBATES, the Bates number of the document's first page, and ENDBATES, the Bates number of its last page.

BEGATTACH is a third field used for document families, most often email threads with attachments. It holds the Bates number of the first page of the parent document in the family, so an attachment three levels deep in a thread can still be traced back to where its family begins. A reviewer filtering by family, rather than by individual document, relies entirely on BEGATTACH being populated correctly.

How Opticon OPT Files Map Bates Numbers to Page Images

Where a DAT file operates at the document level, an OPT file operates at the page level. Each row in an OPT file corresponds to a single page image and lists the page's Bates-numbered image key, the volume it belongs to, the file path to the image, a document-break flag marking whether this page starts a new document, and its page count position within that document.

The image key in an OPT row is exactly the Bates number stamped on that page, which is what ties the physical page image back to the numbering visible when someone views or prints the page. If the OPT file lists ABC000005 as a page image but no page in the actual production carries that stamp, the review platform has an image key with nothing behind it.

Why Mismatched Ranges Break Review Platform Imports

Review platforms validate a load file import by cross-checking the DAT file's declared ranges against the OPT file's actual page keys. When ENDBATES in the DAT file says a document ends at ABC000008 but the OPT file's last page image for that document is keyed ABC000009, the platform either rejects the import outright or, worse, imports it with a silent page miscount that surfaces later during review.

This is why the stamping step and the load file generation step must use identical ranges. If a PDF gets re-stamped after a load file was already generated, for example to fix a typo on one page, the load file has to be regenerated too, because the old DAT and OPT rows now describe a Bates sequence that no longer matches the file on disk.

Building a Load File That Matches Your Stamped PDFs

The safest sequence is to finalize Bates stamping first, verify the ranges using the checks described in our how to Bates number a PDF guide, and only then generate the DAT and OPT files from the finished, stamped output. Generating load files before stamping, or stamping again after load files exist, is the most common source of the mismatches review platforms flag.

For productions spanning many files, apply the same continuous-range discipline covered in our batch Bates numbering guide: lock file order, verify no collisions with prior productions, and only then generate load files against the final, confirmed range.

Common Fields Beyond BEGBATES and ENDBATES

Most DAT files carry a handful of additional fields alongside the Bates range that reviewers rely on daily. CUSTODIAN identifies whose files a document came from, useful for filtering a review by individual. PARENTDOCID and CHILDDOCID track family relationships more granularly than BEGATTACH alone. CONFIDENTIALITY often carries a designation stamped directly on the page, such as "Confidential" or "Attorneys' Eyes Only," which should be tracked as metadata even though it is also visible on the page image itself.

None of these additional fields replace BEGBATES and ENDBATES; they extend the same document-level row with context a reviewer needs beyond just locating the page range. Getting the Bates fields right first matters most, because every other field in the row is indexed against that same document, and a wrong Bates range undermines the reliability of everything else in that row.

Testing an Import Before Final Delivery

Before delivering a load file to opposing counsel or uploading it to a shared review platform, run a test import into a scratch workspace if the platform supports one. Confirm the document count matches the number of documents in the DAT file, the total page count matches the sum of pages implied by the OPT file, and a handful of spot-checked documents open with the correct Bates range visible on the correct pages.

This test costs a few minutes for even a large production and catches the two most common load file errors: an off-by-one range from a late re-stamp, and a broken image path from files being moved after the OPT file was generated. Both are far cheaper to fix before delivery than after opposing counsel reports a failed import.

Background on the discovery and review workflows that these load file formats support is covered in general references such as Wikipedia's entry on litigation support.

Frequently Asked Questions