Aglet

Keep Spreadsheet Date Import Assumptions Visible

The useful lesson is the context required to turn an exported value into the intended calendar date. Record that context instead of retaining only a corrected final value. A future producer or parser change can reintroduce the problem if the import contract still relies on how a spreadsheet happened to display the cell.

Keep the lesson for the next incident

  1. Document representation requirements

    State supported date-text formats, any supported serial convention, and when users must supply format context. Separate date-only values from timestamps. Keep the guidance aligned with preview choices so support does not recommend a serial conversion or date swap that the importer cannot apply under an explicit, reviewable rule.

  2. Retain independently known dates

    Keep a small set of controlled exports with expected calendar values recorded outside the conversion implementation. Include the original ambiguous or serial case and a normal explicit-date control. Explain which assumption each fixture exposes so a future cleanup does not remove the boundary that made the earlier failure observable.

  3. Review producers and date conversions

    Assign review when a new spreadsheet producer, inferred field type, date parser, or timezone transformation is introduced. Compare both the parsed date and representative later use. Track confirmed wrong-date acceptance separately from rejected-format errors so a valid-looking but incorrect calendar value remains visible as a distinct recurrence pattern.

What to carry forward

Close with a source-format contract, known-date fixtures, and an owner for interpretation changes. Preserve missing producer context and historical repair limits explicitly. The next maintainer should be able to explain why an exported number or string represents a particular date without relying on a familiar spreadsheet display or a guessed offset.

Technical background: Microsoft support.

Keep the decision with the work.

Use a Work Item in Aglet to record the problem, the evidence you have, and the next decision. Add an owner and priority, then keep updates in the discussion so the next person can follow the reasoning.

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