diff --git a/student_auto_feed/config.php b/student_auto_feed/config.php
index 5595e2e..2aa4e60 100644
--- a/student_auto_feed/config.php
+++ b/student_auto_feed/config.php
@@ -52,17 +52,35 @@
 // accessed locally or remotely.
 define('CSV_FILE', '/path/to/datafile.csv');
 
-// Student registration status is important, as data dumps can contain students
-// who have dropped a course either before the semester starts or during the
-// semester.  This array will contain all valid registered-student codes can be
-// expected in the data dump.
-//
-// IMPORTANT: Consult with your University's IT administrator and/or registrar
-//            to add all pertinant student-is-registered codes that can be found
-//            in your CSV data dump.  EXAMPLE: 'RA' may mean "registered by
-//            advisor" and 'RW' may mean "registered via web"
+/* STUDENT REGISTRATION CODES --------------------------------------------------
+ *
+ * Student registration status is important, as data dumps can contain students
+ * who have dropped a course either before the semester starts or during the
+ * semester.  Be sure that all codes are set as an array, even when only one
+ * code is found in the CSV data.  Set to NULL when there are no codes for
+ * either student auditing a course or students late-withdrawn from a course.
+ *
+ * IMPORTANT: Consult with your University's IT administrator and/or registrar
+ *            for the pertinant student registration codes that can be found in
+ *            your CSV data dump.
+ *
+ * -------------------------------------------------------------------------- */
+
+// These codes are for students who are registered to take a course for a grade.
+// EXAMPLE: 'RA' may mean "registered by advisor" and 'RW' may mean
+// "registered via web".  Do not set to NULL.
 define('STUDENT_REGISTERED_CODES', array('RA', 'RW'));
 
+// These codes are for students auditing a course.  These students will not be
+// given a grade.
+// Set this to NULL if your CSV data does not provide this information.
+define('STUDENT_AUDIT_CODES', array('AU'));
+
+// These codes are for students who have dropped their course after the drop
+// deadline and are given a late-drop or withdrawn code on their transcript.
+// Set this to NULL if your CSV data does not provide this information.
+define('STUDENT_LATEDROP_CODES', array('W'));
+
 //An exceptionally small file size can indicate a problem with the feed, and
 //therefore the feed should not be processed to preserve data integrity of the
 //users table.  Value is in bytes.  You should pick a reasonable minimum
diff --git a/student_auto_feed/ssaf_db.php b/student_auto_feed/ssaf_db.php
index 9804054..19fec1a 100644
--- a/student_auto_feed/ssaf_db.php
+++ b/student_auto_feed/ssaf_db.php
@@ -175,12 +175,27 @@ public static function upsert($semester, $course, $rows) : bool {
                 $row[COLUMN_EMAIL]
             );
 
+            // Determine registration type for courses_users table
+            // Registration type code has already been validated by now.
+            switch(true) {
+            case in_array($row[COLUMN_REGISTRATION], STUDENT_REGISTERED_CODES):
+                $registration_type = sql::RT_GRADED;
+                break;
+            case in_array($row[COLUMN_REGISTRATION], STUDENT_AUDIT_CODES):
+                $registration_type = sql::RT_AUDIT;
+                break;
+            default:
+                $registration_type = sql::RT_LATEDROP;
+                break;
+            }
+
             $courses_users_params = array(
                 $semester,
                 $course,
                 $row[COLUMN_USER_ID],
                 4,
                 $row[COLUMN_SECTION],
+                $registration_type,
                 "FALSE"
             );
 
diff --git a/student_auto_feed/ssaf_sql.php b/student_auto_feed/ssaf_sql.php
index 34f103b..298e512 100644
--- a/student_auto_feed/ssaf_sql.php
+++ b/student_auto_feed/ssaf_sql.php
@@ -12,6 +12,11 @@ class sql {
     public const COMMIT = "COMMIT";
     public const ROLLBACK = "ROLLBACK";
 
+    // Registration type constants
+    public const RT_GRADED = "graded";
+    public const RT_AUDIT = "audit";
+    public const RT_LATEDROP = "withdrawn";
+
     // SELECT queries
     public const GET_COURSES = <<<SQL
 SELECT course
@@ -72,15 +77,22 @@ class sql {
     user_id,
     user_group,
     registration_section,
+    registration_type,
     manual_registration
-) VALUES ($1, $2, $3, $4, $5, $6)
+) VALUES ($1, $2, $3, $4, $5, $6, $7)
 ON CONFLICT (semester, course, user_id) DO UPDATE
 SET registration_section=
-    CASE WHEN courses_users.user_group=4
-        AND courses_users.manual_registration=FALSE
-    THEN EXCLUDED.registration_section
-    ELSE courses_users.registration_section
-    END
+        CASE WHEN courses_users.user_group=4
+            AND courses_users.manual_registration=FALSE
+        THEN EXCLUDED.registration_section
+        ELSE courses_users.registration_section
+        END,
+    registration_type=
+        CASE WHEN courses_users.user_group=4
+            AND courses_users.manual_registration=FALSE
+        THEN EXCLUDED.registration_type
+        ELSE courses_users.registration_type
+        END
 SQL;
 
     // INSERT courses_registration_sections table
diff --git a/student_auto_feed/submitty_student_auto_feed.php b/student_auto_feed/submitty_student_auto_feed.php
index 5a86ca0..2604984 100755
--- a/student_auto_feed/submitty_student_auto_feed.php
+++ b/student_auto_feed/submitty_student_auto_feed.php
@@ -170,7 +170,11 @@ private function get_csv_data() {
             $course = strtolower($row[COLUMN_COURSE_PREFIX] . $row[COLUMN_COURSE_NUMBER]);
 
             // Does $row have a valid registration code?
-            if (array_search($row[COLUMN_REGISTRATION], STUDENT_REGISTERED_CODES) !== false) {
+            $graded_codes = STUDENT_REGISTERED_CODES;
+            $audit_codes = is_null(STUDENT_AUDIT_CODES) ? array() : STUDENT_AUDIT_CODES;
+            $latedrop_codes = is_null(STUDENT_LATEDROP_CODES) ? array() : STUDENT_LATEDROP_CODES;
+            $all_valid_codes = array_merge($graded_codes, $audit_codes, $latedrop_codes);
+            if (array_search($row[COLUMN_REGISTRATION], $all_valid_codes) !== false) {
                 // Check that $row is associated with the course list
                 if (array_search($course, $this->course_list) !== false) {
                     if (validate::validate_row($row, $row_num)) {
@@ -192,6 +196,10 @@ private function get_csv_data() {
                         if (validate::validate_row($row, $row_num)) {
                             $row[COLUMN_SECTION] = $this->mapped_courses[$course][$section]['mapped_section'];
                             $this->data[$m_course][] = $row;
+                            // Rows with blank emails are allowed, but they are being logged.
+                            if ($row[COLUMN_EMAIL] === "") {
+                                $this->log_it("Blank email found for user {$row[COLUMN_USER_ID]}, row {$row_num}.");
+                            }
                         } else {
                             $this->invalid_courses[$m_course] = true;
                             $this->log_it(validate::$error);
@@ -335,20 +343,12 @@ private function invalidate_courses() {
      */
     private function open_csv() {
         $this->fh = fopen(CSV_FILE, "r");
-        if ($this->fh !== false) {
-            if (flock($this->fh, LOCK_SH, $wouldblock)) {
-                return true;
-            } else if ($wouldblock === 1) {
-                $this->logit("Another process has locked the CSV.");
-                return false;
-            } else {
-                $this->logit("CSV not blocked, but still could not attain lock for reading.");
-                return false;
-            }
-        } else {
+        if ($this->fh === false) {
             $this->log_it("Could not open CSV file.");
             return false;
         }
+
+        return true;
     }
 
     /** Close CSV file */