Insured's policy / group number (with 11a–11d plan block).

The group number from the patient's insurance card. 11a = policyholder DOB, 11b = other plan name, 11c = 'Is there another health benefit plan?' yes / no, 11d = other plan ID.

Box 11 and Box 1A transposed — group number in the member-ID line, member ID in the group-number line. 11c left blank when secondary coverage exists.