keeping track of awe holding

AWE currently holding 57,200,533 shares in ADI (33.792%).

AWE released a "Notice of change of interests of substantial holder form" (Form 604) on 17 May, declaring purchases of ADI shares in May and a purchase on 16/03/10, thereby taking their holding from 32.414% to the current 33.792%. Given that this paperwork disclosed a share purchase dating back some 2 months (16/03/10), how is one to know that AWE hasn't somehow acquired 50.1% from under one's nose (only to let the offer lapse and then disclose this fact some time down the track, as in the above instance)?

I'm sure this is a very basic question, and I'd greatly appreciate clarification. Cheers.