diff --git a/src/main/java/eu/openaire/urls_worker/components/AssignmentsHandler.java b/src/main/java/eu/openaire/urls_worker/components/AssignmentsHandler.java
index e65b4c1..4601ba1 100644
--- a/src/main/java/eu/openaire/urls_worker/components/AssignmentsHandler.java
+++ b/src/main/java/eu/openaire/urls_worker/components/AssignmentsHandler.java
@@ -31,6 +31,7 @@ import java.nio.file.Paths;
 import java.time.Duration;
 import java.time.Instant;
 import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
@@ -226,7 +227,7 @@ public class AssignmentsHandler {
     }
 
 
-    public static HashSet<Long> assignmentsNumsHandled = new HashSet<>();
+    public static final Set<Long> handledAssignmentsCounters = Collections.newSetFromMap(new ConcurrentHashMap<Long, Boolean>());
 
 
     /**
@@ -250,7 +251,7 @@ public class AssignmentsHandler {
             int responseCode = responseEntity.getStatusCodeValue();
             if ( responseCode == HttpStatus.OK.value() ) {
                 logger.info("The submission of the WorkerReport of assignments_" + assignmentRequestCounter + " to the Controller, was successful.");
-                assignmentsNumsHandled.add(assignmentRequestCounter);
+                handledAssignmentsCounters.add(assignmentRequestCounter);
                 return true;
             } else {    //  This does not include HTTP-5XX errors. For them an "HttpServerErrorException" is thrown.
                 logger.error("HTTP-Connection problem with the submission of the WorkerReport of assignments_" + assignmentRequestCounter + " to the Controller! Error-code was: " + responseCode);
diff --git a/src/main/java/eu/openaire/urls_worker/controllers/GeneralController.java b/src/main/java/eu/openaire/urls_worker/controllers/GeneralController.java
index fc7cc7c..5c5718b 100644
--- a/src/main/java/eu/openaire/urls_worker/controllers/GeneralController.java
+++ b/src/main/java/eu/openaire/urls_worker/controllers/GeneralController.java
@@ -94,23 +94,27 @@ public class GeneralController {
     @GetMapping("getHandledAssignmentsCounts")
     public ResponseEntity<?> getHandledAssignmentsCounts()
     {
-        return ResponseEntity.ok(AssignmentsHandler.assignmentsNumsHandled);
+        return ResponseEntity.ok(AssignmentsHandler.handledAssignmentsCounters);
     }
 
 
     @PostMapping("addReportResultToWorker/{assignmentsCounter}")
     public ResponseEntity<?> addReportResultToWorker(@PathVariable long assignmentsCounter, @RequestBody(required=false) String errorMsg)
     {
-        String directoryPath = PublicationsRetrieverPlugin.assignmentsBasePath + "assignments_" + assignmentsCounter + "_fullTexts";
-        File dir = new File(directoryPath);
-        if ( ! dir.isDirectory() ) {
+        if ( ! AssignmentsHandler.handledAssignmentsCounters.contains(assignmentsCounter) ) {
             logger.error("The \"addReportResultToWorker\"-endpoint was called for an unknown \"assignmentsCounter\": " + assignmentsCounter);
             return ResponseEntity.notFound().build();
         }
 
         if ( errorMsg == null ) {
             logger.info("The Controller successfully handled the WorkerReport, for assignments_" + assignmentsCounter + ". The worker-report and all full-text files associated with it, will be deleted.");
-            FullTextsController.deleteAssignmentsDirectory(assignmentsCounter, dir);
+            String directoryPath = PublicationsRetrieverPlugin.assignmentsBasePath + "assignments_" + assignmentsCounter + "_fullTexts";
+            File dir = new File(directoryPath);
+            if ( dir.isDirectory() )
+                FullTextsController.deleteAssignmentsDirectory(assignmentsCounter, dir);
+            else
+                logger.warn("The full-texts directory \"" + directoryPath + "\" has already been deleted by the scheduler.");
+
             FullTextsController.deleteFile(this.workerReportsDirPath + this.workerId + "_assignments_" + assignmentsCounter + "_report.json");
         } else
             logger.error("The Controller failed to handle the WorkerReport, for assignments_" + assignmentsCounter + ". The error is:\n" + errorMsg);