I think TT caches the userID of the person logging into the financial institution. So next time the same user id is used to download it erases all previous downloads for that user ID. Hence the granularity is at these two levels
Financial Institution -> user ID
It does display the different accounts that the userID is associated with and allows you to choose which accounts you want to download. However this last level is not saved in the cache and hence next time you use the same user ID it just erases all previous downloads for that userID/bank
