Unit event data still stored after event state is deleted

No units are being returned between the 1st and 24th January 2018, even though there are units and availability

I'm passing the following into matching units:

Start date is:

$start_date = '2018-01-16 00:00:00';

End date is:
$end_date = '2018-01-19 00:00:00';

Valid states = 0;

$calendar->getMatchingUnits($start_date, $end_date, $valid_states, array());

I've tracked this down to the function in getEventsItemized and itemizeDays in AbstractCalendar.php and its returning a state value that doesn't exist in the db.

Any idea as to whats going on?