To do this sort of thing, you have to be referring to a unique piece of data, or a unique combination of pieces of data. How can a postcode plus a door number be sure of providing such a combination? At the least, you would need an address, door number and postcode, would you not?
Then you could use this combination in the DCount() function to see if the combination already exists...and if it does, retrieve the Record...rather than just populating a new Record with the named fields.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007