Which additional document may be required if applicable, during registration?

The requirement for legal guardian or custodial papers is correct in this context because individuals with intellectual disabilities may not have the legal capacity to register on their own. In such cases, having documentation that establishes the legal guardianship or custody is crucial for ensuring that the individual is represented appropriately in the registration process. This documentation serves to verify that the legal guardian has the authority to make decisions and undertake actions on behalf of the individual with disabilities, aligning registration protocols with legal standards of care and representation.

The context in which other documents may be considered, such as tax returns, voter registration, or employment verification, does not pertain specifically to the registration of individuals with intellectual disabilities. These documents, while potentially relevant in other scenarios, do not fulfill the need for establishing legal authority in the same way that legal guardian or custodial papers do. Thus, they are not typically required in this registration process.