Good Morning All
First up, please call me Zec.
As to the DD's

The DD's had a whole heap of variations over their lives. My current type 1 and type 2 locos really only cover a very small number of locos (but were the main two I wanted at the time

- although I would like to have the others in my collection as well

), namely they cover a total of 4 locomotives now (3 for the Type 1, then the Type 2 covers those first 3 after having the running boards modified and DD 586 in it's as built condition). The type 3 covers a completely different set of numbers, and has the wider cab (along with other changes). Type 4 covers the locos built with the higher running boards, and is essentially going to become the 'base' model to do D3 class locos in future
I never made a CE, or round roof W cars (well I did, but that was almost 10 years ago, and they were just boxes on wheels that looked
somewhat like round roof W cars). See my earlier post about PL cars for info on them. As to the blue and gold car, a private reskin (unreleased) of the CW was done in blue and gold by another Trainzer, but it's not based on any prototype.
For the F horsebox, this was done to simply fill a gap in the rolling stock register to go with my G carriage truck. I really have no immediate plans for the FF, although it is possible in future. As I said, I tend to work on what I want, when I want. Often this comes from flipping through a book and deciding that I like the look of it and then building it. Or just having a desire to have a good quality model of a particular item at the time
Regards