you won't have any problems if your paperwork is in order. If you don't have a police clearance yet I suggest you download the form now and courier it to the SAPS CRC.
unfortunately it doesn't matter how many exemptions and extensions you've had. Everything ties back to that original visa. Fortunately my experience should now save you the expense of a wasted trip to Vientiane.
if you want to stay and work legally in Thailand your only option is to get your visa in SA. One more hoop to jump through, but it will definitely be worth it in the long run.