I have just been through a process to refinance/top-up my mortgage with UBank and they asked for: 1) confirmation of closure letters for each credit card that I had last time but don't have now. 2) confirmation of closure letters for each credit card I have applied for in the last 2 years, but have closed.
I didn't have too many, but for some Ozbargainers that might be a lot of different documents to track down!
If you have the confirmations it is probably not too hard, but I've never documented those, so I had to call up the banks and get them to write something up. ANZ were quick and easy but St George were a bit harder. YMMV with this.
I presume this is due to the new responsible lending requirements, but not sure.
Thankfully I have most of them still, as a matter of habit I scan them and save to dropbox.