The same 'quick search' window improvements that were made to the Work with Input Forms screen were also added to the 'Work with Registrations > Choose Event' screen. The quick search window is at the top of screen. It allows you to search by event title or tag. It will also search the event number field as well. Click the 'x' in the green 'Filtered' button, to easily remove the filter.
Any time a filter is applied using the quick search window, the 'Past Events' list is automatically opened too.