You can assign three titles at max but assigning three titles or more at the same time can create more problems for you.
Problem: You have to manage your precise in a way that your written piece of precise should equally reflect these all three or more titles simultaneously. In my opinion it will be bit difficult for us to manage our precise for more than one titles.

There is no hard and fast rule for single or more than one titles. You can assign more than one outline subject to matching precise material which is quite difficult for us.