Are banks’ systems smart enough to detect multiple switches?

JuicyJesus

If you were with the bank over six years ago it's possible, but you run the risk of the cashback being declined if they do have records. Some of them you would simply never get away with it. Not even six years is long enough in some cases.

Some banks keep limited customer records for quite some time - decades even. Usually just enough to confirm that a person was once a customer and maybe basic personal details, while more specific/"deep" information like statement information is deleted. To put it another way, in my mid to late 20s my previous employer held barebones details of the children's savings account I held with them that was closed when I was 12. American Express are particularly famous for holding a blacklist of defaulting customers that they never, ever forgive and will never allow a card again.

In short you could chance it but you have no guarantee of success, probably no chance of it and would not have a leg to stand on if they did hold any records. Statements and data are also being held for a lot longer because of the risk of future claims against the bank for mis-sale and due to (as masonic says) financial crime regulations, which further reduces your chances of it working.