Yes, and no. I understand and appreciate the site's enthusiasm but think it needs some clarification.
LaVey did search of Satanists prior to him during his occult studies. What he was interested in were genuine Satanist, individuals who proudly accepted the Devil's name and lived accordingly. What did he find? That a "satanist" was a derogatory and biased term used to label heretics and member of opposing religious groups. Jews were satanists, Catholics were satanist, all pre-Christians pagans were satanists. He came up empty.
Keep in mind that this was LaVey in the mid-60's, an autodidact without extensive access to academic libraries and before the internet. Fast forward to today, you have occult and religious studies researchers with access to virtually every book available and advanced search engines, not to mention Google. And trust me, some of these people have no easy feelings for LaVey. And what do they find? A couple of poets and diabolists with no effect past their deaths. They reluctantly have to admit that there was no significant historical occurrence of genuine, self-identified and self-proclaimed, Satanism prior to LaVey. We're not talking about Yezidi, Thelemites, Gnostics, Kabbalists, Pagans, etc. Regardless of what occultists want to call them ex post facto, they themselves did not and do not consider themselves Satanists and would be insulted if you did.
I don't agree with, and I don't think Magus Gilmore does either, that not being in the Church of Satan makes you less of a Satanist. It doesn't make you more of a "free spirited" Satanist either. Now if you go around speaking for Satanism and you're not a member, that's a different ballgame.
"Pretenders To the Throne" was written as a response to materials released by the Temple of Set that claimed some authority over Satanism after their formation. Over some time, and some internal turmoil within the ToS, they let go of that claim and no longer refer to themselves as Satanic or Satanists, but Setian. A more appropriate article would be the Satanic Bunco Sheet, which is a guide for identifying pseudo-Satanists.