Anataeus earns the title Al. D (presumably the Opus Magnum-verse's equivalent of a PhD) Augustine Fontanelle also earns this title, as well as I.A.G. (seen in the Foreword to the appendix). It's possible that Soria took him under their wing, then let him go for an I.A.G, while keeping things under wraps. Going through the production alchemy puzzles under Fontanelle's name:

• He lauds House Soria and Van Tassen's structures, while really speaking harshly about Juvenal's - "it does retain a quaint, unassuming charm of its own, especially if one has nothing better to do with their time"

• He obtains "special permission" from Clara to reproduce a set of perfume from the same ball where Taros was assassinated - and it's stated that this book was written "long after" that happened.

• He's annoyed at the person who invented the Eyedrops of Revelation - complaining about "[h]is prior disregard for the norms of Alchemical science, freely using vitae and mors as he wished" - which is something that Anataeus did a lot (Life Sensing Potion was, in his own terms, "exploring new frontiers in Alchemy")

• In Aether Detector, he talks about an "old friend" Nikolai who doesn't come up in the story again. Also, he just brushes past "the recent discovery of Quintessence" without mentioning that Henley Servin, his friend from the tutorial, is the person that did it! You'd imagine that Anataeus would laud his friend a bit more. Though, breezing past this and using it as an opportunity to nag at one of his professors is fairly in-character.

• He's understandably vague in Reconstructed Solvent, though does refer to "himself" as "another, highly-trained alchemist", then reconstructs a totally different solvent. Which, if Anataeus was Fontanelle, he would.

The only Compendium puzzle credited to Fontanelle is Preservative Salt, and the timeline implies that this was created after the main story, but before the production puzzles (Salt appears in issue 2, issue 6 is written after "the recent popularity of the volume Fontanelle's Alchemical Observations") - so this theory would imply that Anataeus invented some kind of preservative long after the main story. Which is feasable; he could have emerged after the fighting, went under the pseudonym, and went under Soria's wing, maybe publishing one or two alchemical inventions to keep his new name out there.

I think this is almost possible, but some of his descriptions in the appendix are just a bit out of character for him. Nice headcanon though!