If you are using the normal NWN journal/quest mechanism (AddJournalQuestEntry in scripts, the quest settings in conversation nodes etc) then there is already a variable on the PC for that quest so you don't need to add your own.
"NW_JOURNAL_ENTRY" + <journal tag>
is an int on the PC with the current state of the journal with the tag (in the journal editor) of <journal tag>.
e.g. GetLocalInt(oPC, "NW_JOURNAL_ENTRY" + "myfirstquest");