Where do people find all this information about The Weapon ?

For a character in a game yet to be released, we have very little information, but it is quite detailed.

Spoilers ahead I guess

!From the halopedia we have a serial number, confirming Cortana's prediction that she would be replaced by another cortana model AI. Also the fact that she was created to imitate and capture cortana or something similar. I don't remember hearing or reading that in the trailers/sneak peeks!<

EDIT : Edit it seems she says it in an available cutscene. I also haven't finished H5 yet, it's the plan for later today