Cliff said compare real amps to what Fractal provides but we don't have the amps so it is kinda impossible to do as two amps can sound different. But was just reading the
https://www.fractalaudio.com/am4/ page: "Accurate Amp Modeling" and "familiar amp controls behave like the originals". If what we have is accurate to the amps and behaves like them, then it is done! But how can it be accurate but at the same time have these cumulative sound changes? I would like to know what the amp they have sounds likes. I would hope that they pull them out of storage for each update to make sure that they can compare what they are releasing to what they sound like so don't think that would be the challenge. Things like different guitars, playing style etc. would be more of a complicating factor.