I think we're both using the wrong word, as I can't find an actual definition for "cumulative probability". However my formula is what you'd use to calculate the probability of having won at least once over all the drawings.
While you are right that by year five the odds of winning are 9.125%, that is the odds of winning just on the fifth draw. However, you had a chance of winning each year prior, meaning that the odds of winning by year five are higher than 9.125%.
Its like with die, the odds of rolling a 3 is always 1/6, but the odds of rolling a 3 if you roll twice is ~30%.