TL;DR:
Does anyone have a link to documentation explaining the tracing algorithm used by the Demographics Batch Service?
Context:
In our Trust we are trying to use an existing integration with the Demographics Batch Service (DBS) to enrich a large number of patient records (approx. 160,000) with NHS Numbers so that they can be migrated from a Deprecated third party system into our EPR.
Detailed Query:
Our understanding is that matching on postcode is only does positively, meaning that if we have supplied Forename, Surname, Date of Birth, Gender and Postcode (which in our example is overwhelmingly a historical one) for a patient to be traced. If they can be uniquely identified using the names, gender, and date of birth provided but the postcode we provided could not be found on their record in PDS we would expect them to still be matched.
Can anyone confirm this understanding? Or ideally link us to somewhere detailed documentation on tracing can be found 
Many Thanks,
Dave
Hi David,
All the documentation available for DBS is here. Beyond that, you have to continue to send queries through the developer forums.
With regard your query, the behaviour is as follows:
- given a forename, surname, date of birth and gender are found on a single record
- when the postcode provided in the trace is an historic postcode
- then the record will be returned
However
- given a forename, surname, date of birth and gender match a single record
- when the postcode provided in the trace is a postcode with no relation to the record
- then the record will be not returned
I believe that answers your query. Given, as you say, the postcodes provided seem to be historical, it sounds like you should find the patient’s details in those cases.
Hope that answers your query.