I grew up in Ky, & the railroads I remember from my childhood...L&N, C&O, B&O, Monon, PRR, IC, & the SOU Ry...are the ones that I have a soft spot in my heart for.
Since modeling all these RR's would be a much bigger bite than I could chew, I decided to create a fictional RR serving the Ohio Valley, a region where I've spent most of my life, & where all of the above mentioned roads appeared.
So what I came up with was the Kentucky & Indiana RR, a fictional Class 1, circa late 50's-early 60's, straddling the Ohio River from Pittsburgh, to St. Louis, interchanging with all these RR's along the way.
So operating under this premise, in addition to the freelance home road equipment, all kinds of roadnames, from a vast region of North America could show up on my layout, even though the layout itself, only represents a small urban branch of the K&I.
Another thing that I've had great fun with is running cars from a couple of my Gauge friends' freelance roads...
Here's a couple of boxcars...one from Catt's Grande Valley RR, set in MI, & one from Tyson Rayles' Nantahala Midland, set in NC...both htese cars have racked up a lot of miles on K&I trackage!