DarkAngel,
One of the problems with judging a conductor by the number of recordings is that it just doesn't reflect his esteem within the musical community or even his contribution to music. It merely reflects his capacity for self promotion to both the public and the recording companies. When you think of names of conductors nowadays, you think of Boulez, Mehta, Maazel, Levine, Harnoncourt. Of these, how many do you think do not have press agents, music agents, etc. that promote them constantly in order to get them the best deals and the most recording contracts? Boulez is considered a master of self-promotion, and by many musicians as over-rated as well as over-exposed. Now think of Gunter Wand or Herbert Blomstedt, as great as HVK in my book. Both became more appreciated after long careers without generating the frenzy or the multitude of recordings that was generated by HVK.
Von Karajan was such a charismatic figure. He was single for most of his career, endowed with rugged good looks, and a playboy as well with his sexual exploits in all of the German tabloids. When he finally married, he picked a much younger woman of great beauty so that he immediately joined the ranks of power-couples. He enjoyed the type of fame that we associate nowadays with rock stars or in Europe with athletes such as Beckham who also appeals because of his good looks as much as his talent. In Europe, they issued his recordings with such frequency in order to satisfy the numerous fans who were a goldmine for the recording company.
Von Karajan more than any conductor of the 20th century epitomized the self-promoting narcissist. We will have to wait years to see just how much of his work remains in the catalogue and is reissued over and over. Certainly you will not find all of his recordings in print years from now, and as you have found, although you have some of his production, not all is "reference" for you.