Practical Travel Safety Issues - SNN Pre-Clearance

Does anyone know whether all flights to the US from SNN have pre-clearance, or if there are some that do not (and how to figure out which flights those were)?

I would imagine that all SNN flights ate precleared before departure.

There are only 4-5 flights a day (UA to EWR, EI Seasonally to BOS/JFK, and DL Seasonally to JFK) between SNN and the United States.

Also BA's double daily LCY-JFK which has a technical stop at SNN for fuel and US Immigration and Customs. (No SNN-JFK tickets available.)