Why Excel Dates Go Wrong: Text Dates, Serial Values, and Calendar Conversion
Two cells can look like the same date while behaving completely differently. One may be a real Excel date value, while the other is only text.
Keep an original copy, define the rule before processing, and verify the result after processing.
Excel dates are usually numbers
Excel commonly stores dates as serial values and applies a display format on top.
Changing the cell format alone does not necessarily convert a text string into a real date.
Imported dates are often text
Web pages, ERP exports, WMS files, and CSV data can bring dates in as plain text.
Sorting, date subtraction, and pivot tables may fail until the values are converted.
Calendar conversion needs a clear source rule
When converting between local calendar systems and Gregorian years, first confirm what the source values represent.
Keep the original column and create a converted column for easier verification.
Test the result with a calculation
Try sorting, adding one day, or calculating a date difference.
If the value looks correct but cannot be calculated, it may still be stored as text.
Open the matching WUCJ tool and try the workflow directly in your browser.
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