I think what matters for OSM isn't what the railroad designates it, it's what the reality on the ground is. A tiny commuter line that sees a train 5 times a day isn't a main line. (The portions tagged name="Ivy Ridge Line" or now name="Cynwyd Line" do not see numerous trains a day, unless by numerous you mean 5.) A line that hasn't gone to Ivy Ridge since 1986 isn't the Ivy Ridge Line.

I agree that the tail end of the Cynwyd Line (basically after Cynwyd station) is a running line, and I don't object to https://www.openstreetmap.org/way/756330656 being tagged railway:track_ref="Running Track". But I don't think it all matches the description on https://wiki.openstreetmap.org/wiki/Tag:usage=industrial?uselang=en of "railway tracks in private use that serve only freight transport from/to ports, industrial complexes or mining areas, and for connecting these to the public network."