The DSMB's intent for the 75% review is subject to pure speculation so I've made no attempt to guess there. What you surmise may be true and no way for anyone to refute that. What I do know is that the DSMB MUST have noticed a significant number of deaths outside of 28 days of those reported 45 deaths at 50% interim. If there there none or neglible number, then I don't think the DSMB would have requested the 75% look.