If a financial institution receives an NSL, should one presume that it was/is for a customer or previous customer of the institution or is it a "fact finding" mission?

If it is a fact finding mission I am just curious why it wouldn't have been done through 314a.

LEA's submitting names for 314(a) queries have to go through a specific vetting process by FinCEN before the name is accepted. In theory, they have no idea where the person banks and that's exactly what they are trying to determine. It's oftentimes referred to as a "fishing expedition;" i.e. it's like a trawler with 8,000 lines trailing behind it.

The National Security Letter, is a completely internal process within the FBI. They don't need to meet a third party's guidelines. I've never met anyone who claimed significant experience with these devices, but would assume the FBI pretty much knows where the person banks before they issue the letter.

I'm not certain what difference that would make to a bank as there is no connection between these types of queries or crossover between the required responses.