Mr Grim,
although you are quite correct that the term 9 liner is used out in theatre, it is infact incorrect. CAS Briefs replaced them a while back and any reference to a 9 line brief should be in connection with MERT!
Most British JTACs are actually using the correct terminology. Call it splitting hairs however, it makes a difference up in C2 when someone shouts, 'A 9 liner has just come in.'