[MN Renovator]

You can't have much of a party in a 324 sq ft of space. It isn't like putting 10 people in a room immediately creates an unhealthy condition. If the party lasts 3 hours than the standard is cut in half to 7.5 cfm per person. So 75 CFM for 10 people would be adequate for the short period that they are there which isn't even twice the 43.2CFM that your theoretical 18x18 foot box dictates. I have computer fans that push more than this and I'll likely have bathroom fans and kitchen exhaust fans running that will not require any additional ventilation for the house than that. Even if I had 15CFM for my needs and had 20 people in my house for a party, I'm not going to be concerned because any air contamination would take time to occur and since I don't have a party every day, cracking the window a bit and turning on a bathroom fan would be enough in such a demand ventilation requirement. AHRI used to recommend 7.5CFM per person in the 70's, I'd imagine that not every house met that mark, keep in mind a family of 5 may have been living in 1200 sq ft back then or in the preceding decades. My mother grew up in a 1000sq ft house with 5 people, so even with a leaky house, it would have probably been about that if it were reasonably built but hers seemed to be reasonably well sealed, not too many windows, two doors, single story, no attic hatch to be leaky.

Even in new houses with heat exchange ventilation, these systems are designed for the number of people expected to be in the house based on the number of bedrooms and house size with no provision for a party.