Method and limits

Small tests. Clear assumptions.

These notes are an independent reference for diagnosing spreadsheet dates. They are not affiliated with Microsoft or Google.

What was checked

Official Microsoft and Google documentation was reviewed on 8 October 2026. Calendar serial calculations and the fixed-offset timestamp example were independently checked using Python. Formula outcomes are derived from documented behavior; no live Excel or Google Sheets compatibility test is claimed. Menu names and availability can vary by platform or version.

What to preserve

Always keep the source text or workbook, document its date convention, and test a disposable copy. A plausible-looking date is not evidence of a correct import.

Scope

These guides cover spreadsheet values and interpretation. They do not cover calendar-event exchange, recurrence, CSV structure repair, financial decisions, or every historical calendar and time-zone rule.

Privacy in this package

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Source dates

“Reviewed” means the date the sources were checked for this edition. It is not a provider publication date. Provider update dates are listed only when visible in the retrieved source.