I'm not very sure about Word, but Excel 97 onwards, Excel's story around forward and backward compatibility has been very good -- the Excel equivalent of the sc

I'm not very sure about Word, but Excel 97 onwards, Excel's story around forward and backward compatibility has been very good -- the Excel equivalent of the scenario you describe wouldn't happen, because of the introduction of Future Record Types[1]. These are still used in the newer XLSB format[2]. [1] https://www.loc.gov/preservation/digital/formats/digformatspecs/Excel97-2007BinaryFileFormat(xls)Specification.pdf https://www.loc.gov/preservation/digital/formats/digformatsp... (Page 14) [2] https://docs.microsoft.com/en-us/openspecs/office_file_formats/ms-xlsb/abd9c7af-a345-4aaf-999d-8fffa659e6e2?redirectedfrom=MSDN https://docs.microsoft.com/en-us/openspecs/office_file_forma...