SSDI Benefits; Not Enrolled in Part B?

I have a client who is under age 65 and was recently approved for SSDI benefits. Entitled to SS payments as of 3/2014. Her award letter says she is eligible for Part A of Medicare on 3/1/2016, but says nothing about her Part B effective date. She received her red white & blue card in the mail and it only lists her Part A effective date. I am just confused as to why she would not be eligible for Part B on 3/1/2016 given the 24 month rule. Has anyone had this happen before? I have never come across this situation and I work only with those on SSDI.

Source of insurance-forums.net