Don't worry about the case cannelure or lack of it, but if you want best results, consider loading and shooting one headstamp at a time. When you mix up the brass, you'll find (by feel on the press handle) some cases are thicker than others. This will often affect seating depth to the point that it won't be uniform on a mixed batch. Also, again with regard to brass thickness, some cast bullets may be swaged smaller during the seating process because of thick brass.

All this depends on your accuracy requirements. If that's not a big factor, mixed brass won't hurt anything. However, it will never shoot better than segregated brass.