Well this got me thinking that there a three possibilities:
- Making several shadow readings could include too many areas that are above Zone III
- As it is a scan from a negative then your scanning preset might not be correct
- After scanning you moved the shadow and highlights points in to the immediate left and right of the histogram (or similarly used the 'Auto' feature).
So I pulled a copy of your image into Preview and set it to produce a tonally flat file. Doing this shows that you have enough shadow detail so it is your scanning/post production that is at fault. Here for the others is a file that demonstrates what is on the negative:
Bests,
David.
www.dsallen.de