Safe Excel COM writes

The failure this prevents

A COM script sets the cells, Save() returns cleanly, the script prints "done", and the change is gone. The usual cause is that someone had the workbook open in Excel. Their session still holds the old contents and saves over yours the next time they (or AutoRecover) save. Nothing raises an error. Only reading the saved file back shows it.

Related traps that are just as quiet:

• The file was locked, so Excel opened it read-only, and the save never reached the original file.
• GetActiveObject (PowerShell/.NET) or win32com.client.Dispatch (Python) attached to the user's own running Excel, so you edited their in-memory copy.
• Leaked COM references left a headless EXCEL.EXE running that keeps the file locked for the next run.