Using Exiftool. Use command-line to split a string of text in a filename

I’m looking for a way in Exiftool to correctly copy part of the filename into the ‘Title’ metatag of a JPG file.
In a directory I have thousands of files from a database with filenames consisting of a serial number (in this case from A-12669 to A-12673) followed by a surname and first name, and then the .jpg extension.
I want to split this. The filename consisting of the A-serial number plus .jpg extension, and the surname and first name in the Title. I want to transfer a substring from the Name column to the Title column.
So far I have managed to copy it using the following cmd line in Exiftool:
exiftool “-XMP:Title<$BaseName” “-Description<$BaseName” -overwrite_original -ext jpg .
But I only want to copy a substring, from character 9 to the end (without jpg).
exiftool “-XMP:Title<${BaseName;substr(9)}” “-Description<${BaseName}” -overwrite_original -ext jpg .

Apparently this second rule doesn’t work. There’s still something wrong. Who can help me get started with Exiftool? Below are two screenshots.
The first part is of the current directory with the file name.
The second part is of the new directory, where the full string was copied using the above Exiftool command.
However, for the last two files, I manually adjusted the output as desired. So the file name string was split under Name and Title.

Naam                                                              Titel
A-12699 Janssen Jacoba.jpg
A-12670 Janssen Jacobus Hendrikus.jpg
A-12671 Janssen Jan.jpg
A-12672 Janssen Leonardus Hendrikus.jpg
A-12673 Janssen Mathias Jozef.jpg

Naam                                                          Titel
A-12699 Janssen Jacoba.jpg                          A-12699 Janssen Jacoba.jpg
A-12670 Janssen Jacobus Hendrikus.jpg        A-12670 Janssen Jacobus Hendrikus.jpg
A-12671 Janssen Jan.jpg                                 A-12671 Janssen Jan.jpg
A-12672.jpg                                                    Janssen Leonardus Hendrikus.jpg
A-12673.jpg                                                    Janssen Mathias Jozef.jpg