When the BAR's first came, they mainly ran as trailing units on freight runs, most commonly west of Holban. Also as trailing units on the Holban-Ronkonkoma freight (RF-61), and on passenger trains. I remember seeing a Sunday morning Montauk train with C-420, GP-7, GP-7, C-420 quite often. The PNC 1702 worked at the Pinelawn wye when it arrived.
Then anywhere, once the cab signals were installed.