Determine whether or not ChunkLoadEvent is reliable or not.

TestChunkLoadEvent.java

package com.comphenix.example;

import java.util.Collections;
import java.util.List;
import java.util.Set;

import net.minecraft.server.v1_7_R1.ChunkCoordIntPair;

import static com.comphenix.protocol.PacketType.Play.Server.*;

import org.bukkit.Chunk;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.world.ChunkLoadEvent;
import org.bukkit.plugin.java.JavaPlugin;

import com.comphenix.protocol.ProtocolLibrary;
import com.comphenix.protocol.events.PacketAdapter;
import com.comphenix.protocol.events.PacketContainer;
import com.comphenix.protocol.events.PacketEvent;
import com.google.common.collect.Lists;
import com.google.common.collect.Sets;

public class TestChunkLoadEvent extends JavaPlugin implements Listener {
    private Set<ChunkCoordIntPair> loadedChunks = Sets.newHashSet();
    private Set<ChunkCoordIntPair> sentChunks = Sets.newHashSet();
    
    @Override
    public void onEnable() {
        getServer().getPluginManager().registerEvents(this, this);
        
        ProtocolLibrary.getProtocolManager().addPacketListener(
          new PacketAdapter(this, MAP_CHUNK, MAP_CHUNK_BULK) {
            @Override
            public void onPacketSending(PacketEvent event) {
                List<ChunkCoordIntPair> chunks = getChunkCoordIntPair(event.getPacket());
                
                for (ChunkCoordIntPair pair : chunks) {
                    sentChunks.add(pair);
                }
            }
        });
    }
    
    private List<ChunkCoordIntPair> getChunkCoordIntPair(PacketContainer packet) {
        if (packet.getType() == MAP_CHUNK) {
            // Get the single chunk coordinate
            return Collections.singletonList(
                    new ChunkCoordIntPair(
                            packet.getIntegers().read(0), 
                            packet.getIntegers().read(1))
            );
            
        } else {
            List<ChunkCoordIntPair> chunks = Lists.newArrayList();
            int[] x = packet.getIntegerArrays().read(0); // getPrivateField(packet, "c");
            int[] z = packet.getIntegerArrays().read(1); // getPrivateField(packet, "d");
            
            if (x.length != z.length)
                throw new IllegalStateException("Lenght of X was different from Z.");
            
            // Multiple chunk coordinates
            for (int i = 0; i < x.length; i++) {
                chunks.add(new ChunkCoordIntPair(x[i], z[i]));
            }
            return chunks;
        }
    }
    
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        // Print the differences
        if (command.getName().equals("performaction")) {
            Set<ChunkCoordIntPair> missing = Sets.newHashSet(sentChunks);
            missing.removeAll(loadedChunks);
            
            System.out.println("Sent chunks: " + sentChunks.size());
            System.out.println("Loaded chunks: " + loadedChunks.size());
            System.out.println("Missing chunks: ");
            
            for (ChunkCoordIntPair pair : missing) {
                System.out.println(pair);
            }
            return true;
        }
        return false;
    }
    
    @EventHandler
    public void onChunkLoad(ChunkLoadEvent e) {
        Chunk chunk = e.getChunk();
        
        loadedChunks.add(new ChunkCoordIntPair(chunk.getX(), chunk.getZ()));
    }
}

Good news, this appears to have been fixed in 1.7.2:

[16:16:29] [Server thread/INFO]: Sent chunks: 848
[16:16:29] [Server thread/INFO]: Loaded chunks: 1890
[16:16:29] [Server thread/INFO]: Missing chunks: 
[16:16:31] [Server thread/INFO]: ***** lost connection: Disconnected

The load event also counts chunks that are loaded from the MCRegion, but not within range of a player.