This document on the Nassau regiment in Spain has illustrations:
https://www.napoleon-series.org/mili...nChapter3b.pdf
I do not see any shoulder belt plates on their uniforms, but the badge is on page 4.
Next topic to research is the Nassau regiment in the UK.
Their new uniforms may have included shoulder belt plates.
I think they fought at Waterloo.
https://ospreypublishing.com/blog/Wa...e_Bras_Nassau/
One more link:
https://blundersonthedanube.blogspot...-regiment.html