I do not think I can help much more. For some reason the gimpfr.org site does not download for me.
For information, you can often find the script history if you open it in a text editor. Unfortunately Windows does not have great support. You have version 4.0.1 I would not worry about it. Edit: Finally got the 4.0.1 7 zip to download ...and ... photolab_curvebatch.py is still version 3 size 5774 B
This the photolab_curvebatch.py file in Win7 / Gimp 2.8
-----
BIMP
The curve file is made exactly as you show.
In BIMP it is in Color Correction -> and the color curve option.
Works here. Difficult to diagnose with these old setups.
For information, you can often find the script history if you open it in a text editor. Unfortunately Windows does not have great support. You have version 4.0.1 I would not worry about it. Edit: Finally got the 4.0.1 7 zip to download ...and ... photolab_curvebatch.py is still version 3 size 5774 B
This the photolab_curvebatch.py file in Win7 / Gimp 2.8
-----
BIMP
The curve file is made exactly as you show.
In BIMP it is in Color Correction -> and the color curve option.
Works here. Difficult to diagnose with these old setups.