Please be advised there is no 'rule' on turnaround time .... we merely provide some idea of when a CDR applicant may expect an outcome.
As the recent increase form 14 to 16 weeks is primarily brought about by the Christmas/New Year office shutdown period, then your particular application is likely to take about 16 weeks.
Our MSA Booklet is indeed showing 4 weeks - but it is a PDF document, and thus not simple to modify - the advice on the website supercedes this information, but we certainly hope to bring the turnaround time down to this level in the future..