Date Filtering in Ms Access Query (Interesting)

Always handle dates as dates, not strings, not numbers, no exceptions.

And when you write SQL, use the correct syntax. The text expression for a date value must be like mm/dd/yyyy or yyyy/mm/dd.

You did use dd/mm/yyyy, thus your date was read as 2018-02-08. So use:

CDate([a.acdate]) <= #2018/08/02#

and your query will run as expected.