Yes, default value only applies to new records. You'd need a Totals query to count the records for a date. If you want to know for any particular date, create a little form that accepts a date input - the textbox will automatically provide a calendar control if you format it to Date data type or bind it to a date field. You could just use a query parameter prompt but that will allow invalid dates to be entered.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.