From [1] (the meta-analysis), "Working memory interventions proved most effective (g = 0.479), though memory, processing speed, and multi-domain interventions also significantly improved cognition."

From [2] (the crash results), deaths and drop-outs were handled by adjusting crash rates to total person-year exposure times. In this study as a whole, non-completion rates were not significantly different across groups.

Yes, pre-registraton is an excellent idea.