Best UX for incomplete date

Situation: The user entered an invalid or incomplete date into a date picker. For example, the user entered 01/01 then exited the field.

Question: How should the date picker behave?

PrimeNG controls clear the data from the control if it is incomplete.

Angular Material controls make a best-effort attempt to select a date. In this example, Material will have a date 1/1/2001.

NGX Bootstrap selects the month and day entered and completes the date with the current year.

Another option would be to show the control in an error state with a message stating the date is invalid.

User persona: Betty works for a work placement agency. She places workers in temporary jobs at a variety of employers. She enters dates in the recent past, present, and near future for contracts. She is also responsible for entering resume data into the system. This data could include dates far in the past.