Multiple Threads Not Inserting Everything Into MySQL

I am very new to threading. I have a program that calls my api and gets data back in json format. Each request returns a row of data in json format. All together I need to retrieve about 2,000,000 rows a day which means 2,000,000 requests (I understand that this is bad design, but the system was not designed for this purpose it is just what I need to do for the next couple of weeks). When I tried running it on a single thread I was processing about 200 requests a minute which is much too slow. As a result I created 12 threads and I was processing 5500 rows a minutes which was a great improvement.

The problem was only about on average 90% of the rows were inserted into the database as I ran it a few times to make sure. Before each insert printed to a file each URL which was sent and then I checked to see if each insert statement was successful (returned 1 when executed ) and it all seems fine. Every time I run it it inserts about 90% but it does varies and it has never been a consistent number.

Essentially the code starts in main by creating 12 threads. Each thread's creates a run method which calls a new instance of MySQLPopulateHistData and passes a start and end integer which are used in the insert statement for ranges. I have done many system.out.println type testing and can see all the threads do start and all the 12 instances (one instance for each thread) called are executing?

MAIN:

import java.io.IOException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class MainClass {
public static void main(String[] args) {

[code]....