In my setting, the founders of the first transhumanist state, The Consensus, are considered to be somewhere between interesting and wise historical figures to some and are to others something akin to a cyberpunk version of an ancient pantheon. So claiming to be one of these people, a group according to some traditions as small as 10 people, according to others as big as 200 (both definitions are valid, the 10 were the solid core, any others were influential side characters during the solar system era) can be quite beneficial.
Ending the solar system era The Consensus split into the Solaris Confederacy, which stayed behind on Mercury and the emerging Dyson swarm, enforcing the 1000 year-no-interstallar-colonisation-edict on baseline humanity and the Gardener Initiative, which proceeded to colonise the Milkyway and beyond.
As the 25 colonisation fleets left the solar system, those esteemed elders and many others sought to be aboard and to enforce the edict. Luckily this was no problem, as duplication via mind-uploading had been technically viable for two centuries. So versions of each of these founders and often earlier copies where on every fleet and in the solar system. Each time a new star was reached almost everyone stayed there and went forward to the next stars and so on.
This leads to the situation that there is a humongous and still exponentially growing group of people who all have a legitimate and recognised claim to the fame of being one of the founders. Making matters worse, a lot of the founders early lives are widely available as implantable memories or simulation experiences for educational and entertainment purposes. Those are usually marked as such, but the marks could be removed easily by someone dedicating a lot of time and resources to the task.
The basic structures of most human societies are somewhat similar. Almost every settled system has a presence of Consensus Authority, who control the solar laser arrays and some stations. They are still culturally close to each other. Other societies in the systems were mostly founded by those who wanted to try a different social model. This has created many different, yet still somewhat related societies.
Question
How can an imposter be differentiated from the group of people whose claim is legitimate?