Mixed $2 Coins - Forgeries? Errors?

[planchetflaw]

I've probably collected about 15 examples of the following over the years. I've actually picked a few up when buying a train ticket by swapping my $2 coins with people having trouble getting the ticket machine to accept these.

I am trying to work out if these are fakes or a variety of error (struck through oil?).

Attached are some photos. One is my friend's and the trio are the ones I had at work.

Anyone seen ones like this? They are always 1995 it seems.

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[markn]

I am locking this thread.  You should be aware that owning or trading counterfeit Australian currency dated from 1966 onwards is a federal offense.  Remember what you say here is not private.