In the future, you can make spot adjustments by going to
Device Mgt Settings (3 menus down)
Color settings. (you can use the density fine adjustment (dark) to push in those dark blacks if necessary.)
STV +10 works too, but I recommend only using it to a custom paper like stipple or linen where nothing else works.
Also, double check your shade correction a when baselining the machine.
I keep a (best result) shade correction sheet archived. If something is too light or too dark, ill manually adjust until a service tech can further investigate variations in tone.