Soon after the Episodic mappack was leaked back in 2017, attentive users spotted that storyline-related maps of Half-Life 2: Episode One have "point_devshot_camera" entities placed in many different areas. Jackathan decided to write one of Valve employers to learn why they added those entities.
It appeared that those entities take TGA screenshots of places on maps where they are located if you launch the game with "-makedevshots" parameter. After Episode One's development was finished they placed those entities in the maps and then with the use of a special tool they added those cameras on every version of the maps from older game builds. Then they gathered all the screenshots and montaged them on videos to show us how the maps were changed during the game's development. Episode One came out, everyone was celebrating and...Valve forgot about those videos and never released them.
Luckily the employee Jackathan wrote to still had one of those videos and gave it to her, so now we can watch how the map ep1_c17_01 changed during development. At the same time we only can marvel at Valve's carelessness and lack of commitment. Although I'm not sure that anyone still cares after all those years.