I don't think they're unlockable. the List of Hidden Situations.txt file, if it's correct, says that that's it. And also the "Memory" section for CG, pages III, IV and V will forever look incomplete.
Also personally, I'm really disappointed we don't get to see more CG of Kannagi Chiyako, that black hair girl in the YouGate livestream
EDIT: After an embarrassingly short investigation, I was able to figure out what was wrong.
If you're getting the error box at the start, it's probably because you're on Windows 11, because my old college laptop, which is on Windows 10, runs it perfectly fine.
If you're truly starved for oversized breasts, get the trial version and trudge through that.