diff --git a/aprendizations/initdb.py b/aprendizations/initdb.py
index edf7733..9288ebb 100644
--- a/aprendizations/initdb.py
+++ b/aprendizations/initdb.py
@@ -100,19 +100,6 @@ def hashpw(student, pw=None):
 
 
 # ===========================================================================
-def insert_students_into_db(session, students):
-    try:
-        # --- start db session ---
-        session.add_all([Student(id=s['uid'], name=s['name'], password=s['pw'])
-                        for s in students])
-        session.commit()
-
-    except sa.exc.IntegrityError:
-        print('!!! Integrity error. Users already in database. Aborted !!!\n')
-        session.rollback()
-
-
-# ===========================================================================
 def show_students_in_database(session, verbose=False):
     try:
         users = session.query(Student).all()
@@ -120,7 +107,7 @@ def show_students_in_database(session, verbose=False):
         raise
     else:
         n = len(users)
-        print(f'Registered users:')
+        print(f'\nRegistered users:')
         if n == 0:
             print('  -- none --')
         else:
@@ -143,46 +130,67 @@ def show_students_in_database(session, verbose=False):
 def main():
     args = parse_commandline_arguments()
 
+    # --- database stuff
+    print(f'Using database: ', args.db)
+    engine = sa.create_engine(f'sqlite:///{args.db}', echo=False)
+    Base.metadata.create_all(engine)  # Creates schema if needed
+    Session = sa.orm.sessionmaker(bind=engine)
+    session = Session()
+
     # --- make list of students to insert/update
     students = []
 
     for csvfile in args.csvfile:
-        print('Adding users from:', csvfile)
+        # print('Adding users from:', csvfile)
         students.extend(get_students_from_csv(csvfile))
 
     if args.admin:
-        print('Adding user: 0, Admin.')
+        # print('Adding user: 0, Admin.')
         students.append({'uid': '0', 'name': 'Admin'})
 
     if args.add:
         for uid, name in args.add:
-            print(f'Adding user: {uid}, {name}.')
+            # print(f'Adding user: {uid}, {name}.')
             students.append({'uid': uid, 'name': name})
 
-    # --- password hashing
-    if students:
+    # --- only insert students that are not yet in the database
+    db_students = {user.id for user in session.query(Student).all()}
+    new_students = list(filter(lambda s: s['uid'] not in db_students, students))
+
+    if new_students:
+        # --- password hashing
         print(f'Generating password hashes', end='')
         with ThreadPoolExecutor() as executor:
-            executor.map(lambda s: hashpw(s, args.pw), students)
-        print()
-
-    # --- database stuff
-    print(f'Using database: ', args.db)
-    engine = sa.create_engine(f'sqlite:///{args.db}', echo=False)
-    Base.metadata.create_all(engine)  # Criate schema if needed
-    Session = sa.orm.sessionmaker(bind=engine)
-    session = Session()
-
-    if students:
-        print(f'Inserting {len(students)}')
-        insert_students_into_db(session, students)
+            executor.map(lambda s: hashpw(s, args.pw), new_students)
+
+        print('\nAdding students:')
+        for s in new_students:
+            print(f'  + {s["uid"]}, {s["name"]}')
+
+        try:
+            session.add_all([Student(id=s['uid'],
+                                     name=s['name'],
+                                     password=s['pw'])
+                            for s in new_students])
+            session.commit()
+        except sa.exc.IntegrityError:
+            print('!!! Integrity error. Aborted !!!\n')
+            session.rollback()
+
+        print(f'Inserted {len(new_students)} new student(s).')
+    else:
+        print('There are no new students to add.')
 
+    # --- update data for student in the database
     for s in args.update:
         print(f'Updating password of: {s}')
         u = session.query(Student).get(s)
-        pw = (args.pw or s).encode('utf-8')
-        u.password = bcrypt.hashpw(pw, bcrypt.gensalt())
-        session.commit()
+        if u is not None:
+            pw = (args.pw or s).encode('utf-8')
+            u.password = bcrypt.hashpw(pw, bcrypt.gensalt())
+            session.commit()
+        else:
+            print(f'!!! Student {s} does not exist. Skipping update !!!')
 
     show_students_in_database(session, args.verbose)
 
diff --git a/aprendizations/student.py b/aprendizations/student.py
index 8480273..10fad38 100644
--- a/aprendizations/student.py
+++ b/aprendizations/student.py
@@ -174,8 +174,11 @@ class StudentState(object):
         now = datetime.now()
         for tref, s in self.state.items():
             dt = now - s['date']
-            forgetting_factor = self.deps.nodes[tref]['forgetting_factor']
-            s['level'] *= forgetting_factor ** dt.days   # forgetting factor
+            try:
+                forgetting_factor = self.deps.nodes[tref]['forgetting_factor']
+                s['level'] *= forgetting_factor ** dt.days   # forgetting factor
+            except KeyError:
+                logger.warning(f'Topic {tref} is not on the graph!')
 
     # ------------------------------------------------------------------------
     # Unlock topics whose dependencies are satisfied (> min_level)
--
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