Currently there is no check for duplicates when adding contacts as we is done when hiring new worker.
This causes data contamination and a lot more effort from the user since data (like addresses, contact information) will have to be entered once again.
Since functionality, to Check for duplicates and to Merge records manually, already exists in the Globall address book, it seems to be a small step to automate this in the exact same manner as is already done for Hiring new workers.
I can assure that this would improve the user experience a lot ;-)