Since the introduction of the Polymer first circulating series, Australia issued a lot of numismatic products, with dates over print, annual issues with red serial numbers sets, black serial number sets, issues with normal covers, with hard covers, and numismatic commemoratives. Unfortunately many of these were not successful due to overpricing, and many of these were sold to dealers later at a discounted price. At least the bank did not destroy them, not like those NZ annual sets. Now, I believe they are back in demand. Also, for those who got them in a folder, especially those early issues, and if you did not remove the note from the folder, then your note is as good as damaged. If your note is stuck to the bottom of the sleeve, do not try to remove it. If you do, the bottom edge of the note will get very wavy and it will look a bit strange. I believe this is due to the chemical reaction between the polymer note and the glue they used for the sleeve.
As for your A$20, it came in two varieties
1) Standard souvenir - Issue price A$36* Quantity 30,000 sets
2) Embossed folder - Issue price A$69, Quantity 5.000 sets
Note * In my previous post I mentioned A$30