diff --git a/java/src/main/java/org/softwareheritage/graph/utils/FindEarliestRevision.java b/java/src/main/java/org/softwareheritage/graph/utils/FindEarliestRevision.java
index fa02cc1..d9b01ce 100644
--- a/java/src/main/java/org/softwareheritage/graph/utils/FindEarliestRevision.java
+++ b/java/src/main/java/org/softwareheritage/graph/utils/FindEarliestRevision.java
@@ -1,114 +1,132 @@
+// SPDX-FileCopyrightText: (C) 2021 Antoine Pietri
+// SPDX-FileCopyrightText: (C) 2021 Stefano Zacchiroli
+
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 package org.softwareheritage.graph.utils;
 
 import it.unimi.dsi.big.webgraph.LazyLongIterator;
 import it.unimi.dsi.fastutil.BigArrays;
 import it.unimi.dsi.fastutil.io.BinIO;
 import org.softwareheritage.graph.AllowedEdges;
 import org.softwareheritage.graph.Graph;
 import org.softwareheritage.graph.Node;
 import org.softwareheritage.graph.SWHID;
 
 import java.io.IOException;
 import java.time.Duration;
 import java.util.HashSet;
 import java.util.Scanner;
 import java.util.Stack;
 
 /* sample invocation on granet.internal.softwareheritage.org for benchmarking
  * purposes, with the main swh-graph service already running:
  *
  *   $ java -cp ~/swh-environment/swh-graph/java/target/swh-graph-0.3.0.jar -Xmx300G -XX:PretenureSizeThreshold=512M -XX:MaxNewSize=4G -XX:+UseLargePages -XX:+UseTransparentHugePages -XX:+UseNUMA -XX:+UseTLAB -XX:+ResizeTLAB org.softwareheritage.graph.utils.FindEarliestRevision --timing /dev/shm/swh-graph/default/graph
  *
  */
 
 public class FindEarliestRevision {
     public static void main(String[] args) throws IOException, ClassNotFoundException {
         String graphPath = args[0];
         boolean timing = false;
         long ts, elapsedNanos;
         Duration elapsed;
 
         if (args.length >= 2 && (args[0].equals("-t") || args[0].equals("--timing"))) {
             timing = true;
             graphPath = args[1];
             System.err.println("started with timing option, will keep track of elapsed time");
         }
 
         System.err.println("loading transposed graph...");
         ts = System.nanoTime();
         Graph graph = Graph.loadMapped(graphPath).transpose();
         elapsed = Duration.ofNanos(System.nanoTime() - ts);
         System.err.println(String.format("transposed graph loaded (duration: %s).", elapsed));
 
         System.err.println("loading revision timestamps...");
         ts = System.nanoTime();
         long[][] committerTimestamps = BinIO.loadLongsBig(graphPath + "-rev_committer_timestamps.bin");
         elapsed = Duration.ofNanos(System.nanoTime() - ts);
         System.err.println(String.format("revision timestamps loaded (duration: %s).", elapsed));
 
         Scanner stdin = new Scanner(System.in);
         AllowedEdges edges = new AllowedEdges("cnt:dir,dir:dir,dir:rev");
         String rawSWHID = null;
         SWHID srcSWHID = null;
         long lineCount = 0;
+        long srcNodeId = -1;
         if (timing) {
             System.err.println("starting SWHID processing...");
             elapsed = Duration.ZERO;
         }
+        // print TSV header line
+        System.out.println("obj_swhid\tearliest_swhid\tearliest_ts\trev_occurrences");
         while (stdin.hasNextLine()) {
             if (timing)
                 ts = System.nanoTime();
             rawSWHID = stdin.nextLine().strip();
             lineCount++;
             try {
                 srcSWHID = new SWHID(rawSWHID);
             } catch (IllegalArgumentException e) {
                 System.err.println(String.format("skipping invalid SWHID %s on line %d", rawSWHID, lineCount));
                 continue;
             }
-            long srcNodeId = graph.getNodeId(srcSWHID);
+            try {
+                srcNodeId = graph.getNodeId(srcSWHID);
+            } catch (IllegalArgumentException e) {
+                System.err.println(String.format("skipping unknown SWHID %s on line %d", rawSWHID, lineCount));
+                continue;
+            }
 
             if (timing)
                 System.err.println("starting traversal for: " + srcSWHID.toString());
             Stack<Long> stack = new Stack<>();
             HashSet<Long> visited = new HashSet<>();
             stack.push(srcNodeId);
             visited.add(srcNodeId);
 
             long minRevId = -1;
             long minTimestamp = Long.MAX_VALUE;
+            long visitedRevisions = 0;
             while (!stack.isEmpty()) {
                 long currentNodeId = stack.pop();
                 if (graph.getNodeType(currentNodeId) == Node.Type.REV) {
+                    visitedRevisions++;
                     long committerTs = BigArrays.get(committerTimestamps, currentNodeId);
-                    if (committerTs < minTimestamp) {
+                    if (committerTs < minTimestamp && committerTs != Long.MIN_VALUE && committerTs != 0) {
+                        // exclude missing and zero (= epoch) as plausible earliest timestamps
+                        // as they are almost certainly bogus values
                         minRevId = currentNodeId;
                         minTimestamp = committerTs;
                     }
                 }
 
                 LazyLongIterator it = graph.successors(currentNodeId, edges);
                 for (long neighborNodeId; (neighborNodeId = it.nextLong()) != -1;) {
                     if (!visited.contains(neighborNodeId)) {
                         stack.push(neighborNodeId);
                         visited.add(neighborNodeId);
                     }
                 }
             }
 
             if (minRevId == -1) {
                 System.err.println("no revision found containing: " + srcSWHID.toString());
             } else {
-                System.out.println(srcSWHID.toString() + "\t" + graph.getSWHID(minRevId).toString());
+                System.out.println(srcSWHID.toString() + "\t" + graph.getSWHID(minRevId).toString() + "\t"
+                        + Long.toString(minTimestamp) + "\t" + Long.toString(visitedRevisions));
             }
             if (timing) {
                 elapsedNanos = System.nanoTime() - ts; // processing time for current SWHID
                 elapsed = elapsed.plus(Duration.ofNanos(elapsedNanos)); // cumulative processing time for all SWHIDs
                 System.err.println(String.format("visit time (s):\t%.6f", (double) elapsedNanos / 1_000_000_000));
             }
         }
         if (timing)
             System.err.println(String.format("processed %d SWHIDs in %s (%s avg)", lineCount, elapsed,
                     elapsed.dividedBy(lineCount)));
     }
 }