I am a bit concerned that you are only going to use a LAST name and service date.
It is extremely likely that common last names, Smith or Rodriguez for a pair of examples, may have multiple patients associated on any given date. John Smith, Mary Smith, etc. And if you have new born children then multiple births will cause issues.
I suspect that you want at least one other variable. I know that my hospital asks me for date of birth every time they start to do anything: draw blood, take a weight, blood pressure, administer medication ...
Or see if your organization has a patient id or account variable that is supposed to be unique for each patient.
Names are often one of the last things you want to work with if possible. Also some folks change last names, data entry errors.
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