> offline backups are not made after every single transaction.

All you need is an append only tape or even a printer.

Interestingly in the Bangladesh Central Bank hack they used a printer to print out any transactions, but the intruders disabled it or it was just malfunctioning because it's a printer.

But I doubt the Romanians actually had such a system.

In such case notaries (or whoever reports transaction) can resubmit them.

Also, you still have paper documents, kept by parties to transaction, right?