The 3 you quote are the best free resources I know of.
There is another I know of from Cadimage - GDL Handbook.
I see it is now in it's 2nd release and now has a PDF version.
It is not free however and I think is more of an advanced GDL book.
http://www.cadimage.com/Products/Training/GDL-Handbook2
The GDL Cookbook I found to be the best.
A little outdated now but still relavent.
Follow the examples from the beginning and you will learn a lot.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11