Before I give you access, I think I understand the issue now.
1) If we are selecting allowed user roles, for example: Customers, Sales (This means that they are registered users, and this would apply to them only)
2) If we disallow user roles, in this case, distributors (The coupon will work for registered and unregistered users (aka Guest) but not distributors.
3) If allowed user roles are selected, this will automatically eliminate Guest Checkout with this particular coupon because a user role has been defined.
Is all of this correct? If so, I understand where our issues are now.