The claimant, his or her attorney, and all material and necessary parties, shall be notified in writing of the time, place and purpose of any hearing, as well as the evidence to be produced by the claimant or other parties. The notice shall be mailed not less than 10 days before the date of the hearing. In the discretion of the office any issue may be considered and determined, although not indicated in the notice of hearing, if the administration of justice will thereby be substantially served.