In the properties of an EXE file from Microsoft Office and in the about window in Office Online you can find the build numbers that Microsoft uses internally as version numbers. The first block of digits of these numbers, for example “16...”, points to the Office version. Up to and including Microsoft Office 4.3 from 1994, the first digits of the build number corresponded to the Office version.
Since the launch of Windows 95, Microsoft uses year numbers instead of version numbers for marketing reasons. The table shows which build number belongs to which Office version. For some versions, a macOS version of Microsoft Office appeared a little later with the same build number as the Windows version released shortly before.