About all that can truly be said for this "grading" system is that it is unlikely (not impossible) that a seriously flawed component would be given a "Class A" or "B" ranking. BUT: This is really saying extremely little, because the distinctions being made by audiophiles at this level are not about gross questions of competence, they are about relatively slight matters of personal preference and system synergy. With luck, a reader can basically hope to, over time, gain enough familiarity with any reviewer's preferences and language to estimate a degree of trust in respect to that reviewer's opinions having even a somewhat predictable correlation with their own perceptions and preferences, something made wildly difficult from square one just by virture of the fact that there exist limitless system variations within our crucially system-dependent world. But the letter grading system, inherently flawed from the start, has only become more and more meaningless as the years have gone by and the top-rated components have seemingly exponentially multiplied.
Are the reviews and reviewers completely independent? Technically, probably yes - the reviews and reviewers are not operating on a strictly predetermined basis like professional wrestling, or forcibly coerced into their conclusions. But that is not the same as being able to say the deck is not loaded, or that the reviews should be seen as always authoritative. It's called "subjective reviewing" for a reason, and that's the way (highly subjective) most audiophiles seem to prefer it. The opinions rendered in conventional high end reviewing, while their authors may feel they are honestly reflective of what they heard, typically leave so many uncontrolled and dependent variables, fail to to achieve any semblence of comprehensive comparision, are so vulnerable to unconscious bias, are so potentially compromised in integrity by manufacturer influence and benevolence, and are so formulaic in their means of operation and communication, that even with the purest of reviewer intentions - and accounting for the aforementioned overriding factors of listener personal preference and infinite system variability - most cannot be looked at as carrying much more than benign curiousity and entertainment value at best (with the more worthwhile ones maybe throwing in a bit of technical or historical educational value).
This is mostly all OK for the sophisticated reader - especially since in truth any notions of 'real objectivity' are actually unattainable even as theoretical ideals (and furthermore would be fundamentally irrelevent) anyway. But for the novice review reader, you will very likely be swayed by what the 'pros' write, so you can only hope that it will prove to be in the generally correct (for you) direction.
