It is pure speculation on my part about the earliest rail on that section and what might actually have been from the B&S. My guess would be that the straight leg of the wye along side the unloading dock would be the oldest section. The track that was actually B&S would have been along this straight section down to behind Yansick Lumber. The stuff on the wye to the shop would have been BA&A, along with the curve from Yansick up to the interchange. The BA&A accessed the connection with the Pennsy by trackage rights agreements with the B&S. Of course, the B&S ownership of the two roads helped that situation. The BA&A tried their own right of way closer to the creek, north of the current mainline. The battle with the meandering creek won out. Once the B&S built through, there was no need to keep the old R.O.W.
Anyways, back to the original question...there could indeed be sticks of rail that would be old enough to be B&S. Sections have been rehabilitated over the years, such as through the crossings and switches. It would be interesting to walk it and see what the dates are on some of the rail. It is not the oldest section on the whole A&A. Though some of the dates should be 1905-1915 if it were truly from the B&S.