I've seen some crews names written in the cabs of some steam engines. I dont mean graffiti, it's been professionally done. Did one crew always work together on one engine?
Short answer - no. A loco would often have more than one crew in a single journey, especially on longer routes. Firemen weren't always rostered with the same driver either.
Longer answer - some minor rural sub sheds, with only one or two locos, would have had regular crews. Back in the mists of time, when 12 + hour working days were commonplace, again regular crewing of the same loco would have been practical; I've also read of crews accompanying "their" loco to works when it required attention, and helping with the work. Shorter working days, and the need to utilise motive power more effectively, made such practice uneconomic. Some "regular" locos at the top sheds, but again, would be very difficult to manage efficiently.