There are 2 main reasons I have experienced;
- Inability of Issuing authority to make searches and therefore issue certified copies which leaves the applicant with no choice but process the certificate afresh, and
- Fraud: applicant attempting to change some details on certificate and processing afresh to incorporate those changes.
Declarations in my country are often made only when the applicant needs a certificate for some reason. It is suspicious if the applicant cant disclose what they need the certificate for unless it is a routine declaration.
In my country, there are very common names. The order of names, therefore, matters greatly. There is a tendency to start with the surname followed by the first name! this combination of common names and different order of names tends to complicate searches and identification of duplicates. It requires a 3rd parameter to be used in the search to narrow it down for possible duplicate e.g. a date of birth or marriage and place of birth. Furthermore, the absence of permanent places of abode/addresses/administrative units complicates the de-duplication process.
Finally if the system can automatically flag a combination of surname and first name then enable you to correlate with date of birth/marriage and finally place of birth, that would greatly facilitate de-duplication of the registers.