I see things in a very different way. The first two Patriarchs can be viewed as just the splitting up of the Greek and Jewish names of Marcus Agrippa.
Anianus = John (68–82)
The Patriarchs which follow seem to be little more than a confused assembly of prominent Alexandrian figures:
Avilius = Sabellius noted heretical boogieman
Cerdo = heretic associated with Marcion
Primus = 'first' i.e. Mark
Justus = the secretary of Marcus Agrippa. I note the similarities between the two figures in my book.
Eumenes is probably an actual person. Might even have been the unnamed Patriarch referenced in Hadrian's Letter to Servianus - "And after a lapse of a year and some months, Eumenes (q.v.) succeeded in the sixth place to the presidency of the community of the Alexandrians" [H.E.IV.5.5].
Markianos or Mark (the tradition is unclear). Could be the historical figure associated with the 'Marcion' who visited Rome in the middle of the second century.
As you might know I think that Demetrius election was imposed on the Alexandrian community and Clement and Origen likely represented crypto-Patriarchs or Patriarchs in exile. The only reason that the 'Origenist' Patriarchs that followed were likely only allowed to flourish because of the fact that Rome was losing control of Alexandria.
The situation in Alexandria regarding their 'remembrance' of who Mark was is no different than what we find among the Samaritans. If you hit someone over the head long enough they will lose consciousness and even forget their own identity.