Testing a component that appears repeatedly in the code - Test once per component, or per appearance?

I am doing testing on software used in clinical trials.

There are components that are repeated throughout the forms. For example, there is a date component that appears repeatedly across a number of forms. It has some peculiarities such as accepting UNK in the month and day fields.

Does this field need to be tested new each time it appears? I am told that from a regulatory standpoint each instance must be tested for all possible cases individually, even if the code is replicated across the forms.

Does anyone have any insight on best practices here? I am overwhelmed by the amount of work it will take to confirm the proper functioning of each field individually.

Thanks for any advice!