I am not an expert, but as a collector, these are the two main thingy that I would look at as and when I get hold of an Australian polymer note.
First – The year the note was printed. Since you have got this recently from the bank, I believe you must have got a 2008 print, or maybe a 2007 print. To find out in what year this note was printed, just look at the first 2 digits numbers after the two letter prefix. It should be 08 if it was printed in 2008, or 07 for 2007 etc.
Then look at the letter prefix. For all polymer notes issued since 1993, all first prefix are represented by the two letters AA, with the exception of the $5 (first prefix BA). Unlike collectors in Canada, I am not sure if there are that many collectors going for all prefixes issued. This can be an extremely difficult task for collectors here to achieve that.
Generally first and last prefix are the notes that command a premium here in Australia. And in most cases, last prefix costs a bit more as in some of the earlier issues, collectors were not aware of these prefixes and by the time they found out, it’s already all gone into circulation, thus finding one in UNC condition was hard but not impossible. Even those issued recently can still fetch a pretty good price too. For example, the 2008 $50 last prefix was MD08. Less that 50,000 printed for this prefix, and some dealers are now selling this note prefix for $150 each. As for the $50 AA08 first prefix, you can still get them for less than $100.
There is no replacement notes printed for the polymer notes, and to me every last prefix notes printed are more or less the replacement notes, after all they to print certain quantity to take the consideration of errors and rejects during the printing process.
I hope you like the $50 note. Consider yourself luck, as for me to walk into a local bank and ask for $50 note in UNC condition, chances are I will not get one. Not even on ATM.
If you want to know more about this $50 notes, here are the 2 links that can tell you more about this note; -
http://australiapolymernotes.blogspot.com/2009/10/fifty-dollars.htmlhttp://australiapolymernotes.blogspot.com/search/label/Fifty%20Dollars%201995Have fun and enjoy.