Primary Key duplication

I am creating a database where the primary key will sometime be duplicated, but the data itself will be different; can I do this by index yes allow duplicates? I am using subforms; If I have another record with demographics that are the same and the same account number, but some of the data is different, how can I create it so that the demographic data will be the same, but add the different table content?

Thank you so much in advance.