Dark chocolate describes a style, not a guarantee that the bar is vegan. Some products contain milk ingredients, and formulations can change between varieties from the same brand.
Read the ingredient list each time you buy for a recipe with specific requirements. A vegan label can help, but it does not mean the product is suitable for every allergy. Precautionary statements and individual needs still matter.
For baking, notice whether the recipe asks for a bar, chips, or cocoa powder. They behave differently: some chips are designed to hold their shape, while chopped bars melt into softer pockets.
Taste the chocolate before committing a whole batch to it. Very bitter chocolate may need a recipe designed around that intensity. Changing the cocoa percentage can affect more than appearance, particularly when chocolate makes up a large part of the dessert.