I don't know that anyone but the airline would know that information. Equipment swaps happen all the time, even when the flight number does not change at a stop. I have often seen the second leg of a flight leave before it arrives - such as:
NW1234 Departs XYZ 10:00, Arrives ABC 11:00
Status Delayed: Est. Dep 12:00, Est Arr 1:00 Gate A2
NW1234 Departs ABC 11:30 Arrives PQM 1:30 - On Time Gate A99
For hub and spoke airlines it can be easy to tell at the "spoke" airport if the flight arriving at a gate is late, the next flight leaving from that gate (and same equipment) will also be late. At the hub the greater availability of equipment means a swap could happen, so I would not trust watching the inbound.