I tell myself I'm modeling about 1952. On the NYC portion of my layout, I stick to 1948-52 pretty well, I do have a 1938 20th Century and I will have at least one 60's era freight, because there is some 60's stuff I can't resist. But if I ever have a "serious" operating session I'll just run the 1950 time frame stuff. I have a bigger problem maintaining a time frame on my JGL, as I just had to have 1990 Susquehanna locos, said road has trackage rights into Taylor yard (in the 50's too with RS1s) Locos built in late 50's and early 60's will be allowed even during 1950 operating sessions, lettered for JGL with their "Ahead of our Time" logo. My biggest hurdle is operating steam on a 1952 JGL, as it is supposed to be a "progressive" modern road, early to switch to diesel. But I love steam, and so does the Vice President of the JGL, Eddie Willers, luckily. So he has kept some JGL steam and has been purchasing other roads steam for next to nothing as it is about to be scrapped. He maintains them with his own money and assigns them when he wishes. They are only run between Trenton and New York State's Taylor Yard, where they are kept. This is why, of course, I elected to model this portion of the road. The President had some misgivings about the presence of steam on his road, but the VP runs an efficient operation and doesn't allow the steam to cost the railroad anything, and the public has really taken to it, ridership of the railfan trips behind an old 4-6-0 is always high. So it seems as long as Mr. Willers is willing to finance them, steam will be present.
Funny the lengths we go to to justify doing whatever we want!