I'm still leaning towards BLAB sending out defamation cease and desist letters.
After rereading Adam's very carefully worded hostage style statement, I think you nailed it.
Perhaps, Adam being a trusting/good natured guy may have not required Katie & Spencer to ever sign a formal sublease agreement contract that outlined obligations if the sublease was terminated early:
A) He's a trusting friend.
B) It would have probably required some formal sign-off by his Landlord who may have then charged extra administrative fees for additional background checks, writing up an amended lease, etc.
C) Katie and Spencer perhaps manipulated him to skip all of that because neither of them wanted to be in a legally binding lease either.
They then potentially used the same "formal legal actions" that would have protected Adam's interests when they broke the sublease to then go after Adam for him eluding that they broke a sublease that they never formally had.
Pixar Charlie/McKenzies/Dylan/Brickey aka Adventures in Design aka Hey Brickey aka Brickey Talks Disney aka bricKAI,
If they will betray and strong-arm Adam the Woo (and his 678k Subs) with the quickness/tomfoolery, think what they would do to you if given the chance to reach higher by stepping on your necks?