#4 The winner didn't main event WrestleMania until 1993
We should clarify that main eventing WrestleMania wasn't a condition of a Royal Rumble victory until the 1993 edition of the event; Hulk Hogan won the 1990 and 1991 Rumbles, and would close out the WrestleMania broadcast in both years, but neither year had a connection between the pay-per-view events (although Hogan was the challenger at WrestleMania VII in 1991 after winning the Rumble, that was more in line with Hogan defending America against the evil Sgt. Slaughter than it was Hogan earning a title shot by outlasting 29 other men).
It wasn't until 1993, when Yokozuna won the sixth televised Royal Rumble match, that the winner was guaranteed a number one contender spot for the main event at WrestleMania; that accolade has continued for the past 25 years with very few exceptions. The championship opportunity is transferable in storyline, and is often defended at the February pay-per-view; the win also does not guarantee that a winning superstar will be the only challenger for the belt, as numerous WrestleMania main events have seen triple threat matches where the champion and Royal Rumble winner are joined by a third competitor.
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Male superstars are 14-10 in the resultant championship match at the Showcase of the Immortals (women, so far, are 0-1, as Asuka lost to Charlotte Flair at WrestleMania 34); two men's Royal Rumble winners (Steve Austin in 1997 and Vince McMahon in 1999) did not receive their WrestleMania match, the former because he re-entered the match after being eliminated and the latter because he renounced the title shot the following night on RAW is WAR.