Problem solved!
Michel was partly right, but so was I. It turns out that the difference was that I was running Microsoft's .NET 3, and it looks like you need .NET 4 in your VB.NET application, which has more tags.
So I spent a lot of time searching the Internet for a tool to get lots of picture tags. Turns out that apparently the best picture tag software tool out there is called ExifTool, since it can read a wide variety of tags, like EXIF and IPTC. Importantly, it comes with a standalone executable version AND a DLL version that can be included into .NET applications - like Microsoft's VB.NET. Check out ExifTool.org for details on it. Then one person (Curtis) on their forum at exiftool .Net wrapper (written in vb.net) created a way to easily run this tool from within VB.NET. So I downloaded the EXE and the DLL and inserted the DLL into my VB.NET app, then did testing.
Confusingly, the tag I'm looking for, Adobe's Descriiption Writer, seems to go by several names. The spec at IPTC Photo Metadata Standard 2023.1 confirms the tag name I was looking for. But, the ExifToolIO routine I downloaded doesn't know it by this name. Instead, it's called Writer-Editor, and is retrieved by the following routine call:
ExifToolIO.Cmd("-Writer-Editor")
(users familiar with this routine will note that you can drop the tag class prefix that goes between the dash and Writer-Editor, simplifying the call).
So there you have it. In summary, the tag Adobe calls Description Writer can be read from within a VB.NET program using a utility that has both an EXE and DLL, and the tag is called Writer-Editor.
By @don-peters
I am glad you have found your way to automate the description writer tag.
I still wonder how useful that tag is if it's only to write that tag, which is available directly in the organizer (IPTC) and the PSE editor (file info)
I seem to remember that you can assign a template for your own tags (mainly descriptions and copyright) when you import files. I'll have to do some search and tests...
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