compare windows tagging to exiftool tagging

[Nexius2]

hello,
I'm trying to add a title to a picture so that my photo library can display it.
when I add the title via windows, the library displays it correctly.
when I look at the file, I see that windows changed XPTitle, Title, ImageDescription and Description.
so i thought I could do

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exiftool -v -overwrite_original -XPTitle="my title" -Title="my title" -ImageDescription ="my title" -Description="my title" photoname.jpg
it actually changes the right lines but my library won't get the title
so I tried to compare the to files with

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exiftool a.jpg b.jpg -a -G1 -w txt
diff a.txt b.txt
but all I could see was

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+[XMP-dc]        Title                           : My Title
+[XMP-dc]        Description                     : My Title
I tried to add -xmp:Title="My Title" but doesnt change...

I see no other difference between my exiftool command and what windows does.

any guess?

[Nexius2]

I'll answer myself.
there where no difference, My library just seems to remeber photos and take info from the database.
If I do a

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exiftool -v -overwrite_original -ImageDescription="My desc" -Description="My desc" myfile.jpg
before adding the picture in anyway in my library, I end up with what I want.