Automatic Numbering does not recognize my privately created style:
Cell[StyleData["Exercise", StyleDefinitions -> StyleData["Text"]],
MenuSortingValue->10000]
also tried the following modification:
Cell[StyleData["Exercise", StyleDefinitions -> StyleData["Text"]],
CounterIncrements->"Exercise",
MenuSortingValue->10000]
In either case, invoking Insert>Automatic Numbering (and selecting style Exercise) produces 0