The British source to the counterpunch.org article was a transcript of a session in British parliament. I will assume that the transcript has not been falsified, The tables in the transcript show in no uncertain terms that Clinton’s tonnage for 1999-2000 was 535 Mton << 1464 Mton. I believe this source, I don't see any reason to find another source.
One could speculate how counterpunch came up with 1.3M. I suspect they double-counted by adding up both quarterly and yearly numbers. That is a big mistake. They may also have counted the UK contribution multiple times.
>>I will prove the point, and I will find the sources to do so.
This is not a good approach, I think. One should first find the correct sources, and then draw the appropriate conclusions, and not the other way around.