Formula Queries - Entering Duplicates

I have a Clients table where Record ID# is the key field. My goal is to prevent a User from adding a Client that already exists in the system. I've set up a data form rule that works great for preventing a duplicate record from being added if the SSN entered already exists. However, if I want to go into an existing record in Edit mode to update any other personal information such as an email or phone number, I cannot save the record because the system thinks that the current record I'm in already exists, which it does but I'm not "adding" a new record, I'm merely editing one. Below is the formula query that I'm using directly from the QuickBase training video: 

If(
Size(GetRecords("{22.EX.'" & [SSN] & "'}"))
> 0,
"A CLIENT ALREADY EXISTS WITH THIS SSN."
)

I've tried manipulating the ">0" portion of the formula but nothing seems to work. Any help would be greatly appreciated!

------------------------------
Todd M.
------------------------------