My guess is that questionnaires won’t only have been sent to those who are known to have been present at the gatherings. If for example you think of the ‘bring you own booze’ event, the email invite went out to 100 people, but only 30ish attended. The other 70 are unlikely to toe the party line because they thought it was wrong to attend in the first place. Also, one or probably more people are leaking information to the media, and they no doubt have a group of allies providing them with information - and photographs. It’s a very tangled web, but ultimately the PM is a trapped fly.