The door swung open at once. A tall, black-haired witch in emerald-green robes stood there. She had a very stern face and Harry's first thought was that this was not someone to cross.
"The firs' years, Professor McGonagall," said Hagrid.
"Thank you, Hagrid. I will take them from here."
She pulled the door wide. The entrance hall was so big you [A] could have fit the whole of the Dursleys' house in it. The stone walls were lit with flaming torches like the ones at Gringotts, the ceiling was too high to make out, and a magnificent marble staircase facing them led to the upper floors.
They followed Professor McGonagall across the flagged stone floor. Harry could hear the drone of hundreds of voices from a doorway to the right –– the rest of the school must already be here –– but Professor McGonagall showed the first years into a small, empty chamber off the hall. They crowded in, standing rather closer together than they [B] would usually have done, peering about nervously.
(Harry Potter and the Sorcerer’s Stone, pp.113-4)
When I interpret [A] into my own language, I’m urged to add an intensifier onto the phrase - this intensifier is a suffix (도) which intensifies a case that has an unexpected or exceptional property. So I get a curiosity whether the English, could have fit, really has the intensifying meaning. If it has, does it come from the structure - doubly remoted construction: could + have + p.p. - itself or from the context? (When I look at this, [B] would usually have done, this seems not have the intensifying meaning.)