There is a limit on codes you can put in based on the first four letters so everyone needs to know to make sure they are not maxed out on the codes already.
You can no longer merge two vudu accounts been disabled for months, you can no longer egift movies with credits as of a last weekend and confirmed by vudu 3 days ago. And you only have a max of so many UVVU slots, so you can only merge a few vudu account via those means at the cost of preventing future people from merging on your family account. So creating other vudu accounts to get around max redemption isnt ideal for everyone.