Why the receipt matters more than the bank line
A bank line proves money left your account. It does not prove what it bought, whether it was for the business, or how much VAT was on it. Only the receipt does that, which is why HMRC asks for receipts rather than statements.
Most lost claims are not aggressive ones. They are ordinary costs whose evidence faded, went in a bin, or stayed in a jacket pocket until nobody could remember what it was.