Why change the story just to fit in one specimen? sounds like too much work to me. I don't think you should ever change an original story just to make something fit. Defeats the purpose of having a story.
I didn't realize the story was canon. Anyway, no one is talking about uprooting the entire KF universe. Maybe Dr. Zvletski worked for Whatshisname. Maybe Dr. Zvletski had a parallel project going as well. Or maybe we just kill off Dr. Zvletski altogether. Focusing on Dr. Zvletski making Marhithera seems like such a tiny nit to spend time on.