Yes, the Boolean expression "A and not A" is by definition always false.
Creating a second saved search is the easiest.
Another way would be to make a saved search:
Code:
#read:yes
AND #percentread:100
AND (#lastread:=thismonth OR #lastread:>14daysago)
For this example I name this search "reading_base".
Now make two saved searches:
Code:
search:"=reading_base" AND #fanficstatus:"=In-Progress"
and
Code:
search:"=reading_base" AND NOT #fanficstatus:"=In-Progress"