REA vs. LCL vs. "Express Freight"
Railway Express Agency (REA) was the railroad owned equivalent of UPS or FedEx. Railroads worked together to handle small parcels in an express manner (ran on passenger schedule). PRR listed these cars as "Passenger Service" (IDK if all roads did this or not). These cars would sometimes run in their own train, or as 'head-end' on a passenger train.
Less than a Car Load (LCL) was more for shipping 'widgets' and such. Shippers that had less than a full car load would be combined together and charged less than a full car cost. The fully loaded car would be handled like any other general freight service, this was not an express service. The car would be shipped to a freight house, where the contents would be sorted and then either loaded onto another LCL car, stored for later shipping, or loaded onto a truck/given to the recipient merchant.
Express Freight - Merchandise Service (PRR) / Pacemaker (NYC) / Sentinel (B&O) was a freight delivery service that ran in an express manner. Cars we designed to run at higher/passenger speeds, but were not put in a passenger consist. While the loads might be LCL, they were not (just) a LCL service. They did not leave the 'home rails'. (I have not been able to determine if they were given the same/similar priority as passenger service.)
notes/improtantt stuff here