A few questions/things to think about.
Could the problem lie in the data you have? Does that entry where you're seeing ZZ9906368... actually need to have ZZ990895425... or something like that?
How long are the bank numbers supposed to be? You've got an example with a nine digit number and an example with a six digit number. In the US, for example, all routing numbers are guaranteed to be nine digits. So, if you give a similar set of strings like your post suggests you have, I know that I can slice a string at the same place each time to get the routing number. E.g., nfRoutingNumber.slice(5,13) would give me the routing number without having to do any extra searches. Are you able to do that? Or are the numbers you're searching for going to get you do a different number that might be a different length?