Etapestry's 'DIY Forms', which we use to take donations, struggle to deduplicate existing donors and instead make brand new Constituents from people who may already exist on the database.

I would ask that deduplication include the Postcode field to help improve this. Deduplication is currently done against Name, Address Lines, and Email address.

If any of those are different eg they give their full first name instead of an initial (the information about it online is incorrect), put a comma/typo in the first line of their address, or give an email where we had none in the record, it will create a new Constituent. Using Postcodes would help as they have a very fixed format and are usually specific enough to an individual.