I have several engines that are the same by plan. When I started my 027, 28 switch, operating layout in 1976, I got four mostly plastic Lionel 2-4-2s, Marx 999, and 666s as I needed four to run on the layout at a time. I moved up to 2026 2-6-4s as they pulled better and got four or more. Later I moved up to 2035s as they pulled better and I had many heavy operating cars so I have probably six of them. Being postwar, all cost $35 or less and all cost less than one of the new $600 plus engines.
Of course, the number on the cabs is not important to me, at least not enough to re-number them.
Charlie