I have modelled different time periods in the past, and as such have various stock from these different periods. I was initially going to stick to a strict time period, but I could see this being too frustrating for me! How could I run Early AC electrics in BR Blue, and 87030 in Virgin livery for example? It was then decided to operate the layout in different periods.
The main period modelled is generally late 80`s / early 90`s, but operating sessions could see stock from the early to mid eighties operating one week, gradually moving on in time over operating sessions, and then a smooth transition back again. Sticking to these simple rules, most trains should be in period with no major clashes, and over the weeks a slow transition can be observed.
Hopefully the diagram below can help explain what I`m getting at.....