Board Thread:Introductions/@comment-2188103-20170813171926/@comment-16461120-20170814180826

The exceptions you noted regarding military personnel and informants all have verifiable identities which are known to authorities, so they're not exactly secret, merely not part of the public record.

In universe, as pointed out in the current Daredevil arc, while the names Steve Rogers and Tony Stark might not have been public knowledge until after the turn of the century, the authorities and other established heroes could presumably verify their identity in private to the satisfaction of a theoretical court, the problem for Matt Murdock is that virtually nobody remembers what the Purple Children erased, so he couldn't be confirmed by a figure of authority so that his true identity would be considered confidential in the same way.