Apologies in advance if this ends up being a silly question (I'm probably not as informed on railways as most people here) but I was on an LNR service recently (15th June) and while I was aware of the existence of the terminating platforms at Northampton, I was under the impression that they were not in regular use and only the Birmingham-Euston services called there using platforms 1 and 3. However when stopped there the other day I saw an LNR 350 at platform 5, with the destination displays showing 'This part to Northampton'. I couldn't see anything on realtimetrains that might correspond to it, does anyone know what this was (and if these platforms are actually used after all)?