I need to beam real Portal trivia into the brains of people directly because GOD every time I see something online about this game there's always at least someone being so confidently incorrect or missing just one specific fact and AAAA I hate it when people are wrong about the stuff I love.
There is no testchmb_a_12 map in Portal 1 despite there being an 11 and a 13. This implies that a chamber between 16 and 17 was developed at some point but scrapped. (the discrepancy in the numbers is due to the fact that some maps contain multiple chambers but you already knew that)
A couple more fun map facts about Portal 1 include: The Transmission Received radios aren't part of the maps but instead generated at runtime from a resource, there is a big invisible box around everything that isn't the GlaDOS fight in escape_02 which destroys props, the debris from the cube dropper in the escape section of Chamber 19 can actually activate the button and speaking of buttons, turrets named box can activate buttons but the first turret you encounter in Chamber 16 is named training_turret so it can't do that. The game does some more stuff with the names of entities but this is the most noteworthy thing.
I'm a filthy casual so I knew none of that!
I only get that deep into Undertale/Deltarune.
Tell me more?
I'm not at home so this is just a mini-fact, there are several unused voice lines in the Portal 2 files in which GLaDOS directly refers to Chell by name including a particularly blood-chilling one in which GLaDOS alludes that this is the last time Chell's name will ever be said. There are also some terrifying lines of Caroline being put into the computer against her will. According to some developer comments, GLaDOS used to be much more mean at some point in development and, this isn't a cool portal trivia fun fact, I want to have what Ellen McLain had when reading her lines.