The game you want to create a mission for determines which version of Dromed you can use.

Maybe a history of Dark Engine tech could go here?

Thief 1 and Thief Gold use a monochrome light engine with 256 levels of brightness.

1.33

The first publicly available version of Dromed.

1.37

The version of Dromed released with Thief Gold. There were no significant differences between version 1.33.

was there a version prior to 1.33?

Thief 2 introduced colored lighting, but reduced the bit-depth to just 5 bits per channel.

1.07

The initial version of Dromed for Thief 2.

1.18

This version fixed some bugs. The update was not compatible with missions created using version 1.07.

System Shock 2 is similar to Thief 2 but has a different style of game play.

2.12

Dromed for System Shock 2 is often called “ShockEd”.

New Dark is an unofficial modification of the Dark Engine that can play Thief 2, Thief Gold, and System Shock 2 missions. Missions built with this version of Dromed will not work in legacy games, but missions built with earlier versions of Thief 2, Thief Gold, and System Shock 2 can be edited with New Dark. The initial release of New Dark for Thief was 1.19 and for System Shock 2 was 2.40

1.21

The latest version of New Dark for playing Thief 2 and Thief Gold missions. Missions built with this version of Dromed will only play in Thief 2 mode.

2.42

The latest version of New Dark for playing System Shock 2 missions.