I have some lenses (Nikon 35mm and Pentax 55mm) that are identical other than having single-coating (thoriated glass) or multi-coating (non-thoriated glass).
The multi-coated versions all have a little bit more saturated colors. Other than that I have never noticed a difference.
https://talktog.wordpress.com/2013/08/15/lens-review-leica-l...