I'm working on a personal project that has required me to create a list of all of the events I've worked. I'm doing this to the best of my memory, but it's becoming increasingly hard to recall events over the past eleven years, especially some of the smaller assignments. Just at New York Road Runners alone we held 55 road races each year, and each of the Events team worked ~40 of them per year. The same thing when I was at Disney Sports in its early existence and we didn't have the number of staff they do now to manage and work the 200+ events. A lot of us played different roles in a lot of different events other than the ones we managed.
Last year, I advised one of my staff who had been at NYRR for eleven months to list all of the races she'd worked and briefly describe what her responsibilities were for each race. (Turns out she'd worked 42 races in 49 weeks.) The reason for the exercise was for her to have them as she updated her resume. She could then easily choose which ones she wanted to highlight on her resume. I wish I had been smart enough to keep track of everything I had worked or for which I had volunteered. It would have been easy, just a simple Word or Excel document updated each week or month. It also would have made it easier updating my resume through the years and also to recall specific examples for interviews. Something to consider as you start.