It's an insult. If someone (who isn't John, Paul, George or Ringo) calls you a fifth Beatle, they're not being nice.
For fifty years, people have been proclaiming that they're intimates, part of the story, a key component of the success of the Beatles... Just as there are people who would like you to believe that they were instrumental in this startup, that project or the other initiative. Success has many parents, failure few.
Here's the deal: you don't get to be part of the success narrative unless you were fully exposed if there was going to be a failure narrative instead.
Innovators need your support, without a doubt. But if you want to be a Beatle, start your own group.