A question on ELU (“Sassanian” vs. “Sasanian”) brought up the fact that the name of Sāsān has often been spelled in English with a double S in the middle: "Sassan". (The same goes for related words like Sassanid.) This is a bit mysterious because as far as I can tell, the name is not pronounced with long /sː/ in Persian (nor is there any evidence that it ever was—if I'm wrong about that, though, please let me know!).
I am wondering what kind of precedents, if any, there might be for this spelling in Latin or in Greek. I tried to research this a bit for my answer to the linked question, but I didn't find out much; however, I am reproducing my findings in this question.
The etymology section of the Oxford English Dictionary entry for the English word Sassanid seems to indicate that -ss- spellings of related words existed in medieval Latin: supposedly, Sassanid comes from "medieval Latin Sassanidae plural, < Sassan, Sasan". But I haven't been able to find any more sources that explain why -ss- might be used in Latin Sassanidae. I know that medieval spellings were often variable, but I don't know if the use of -ss- here ought to be explained as just a meaningless alternative to -s-.
Varro's answer here suggests that Greek -σσ- (rendered in Latin and English transliteration as -ss-) may have been used in the transcription of non-Greek certain names to represent some unclear difference between sibilants in foreign words and the sibilant /s/ sound found in native Greek words. For example, it seems the use of -ss- in the modern English spelling of the word "Messiah" can be traced back to Greek.
However, I can't find any resources that attest to the use of spellings with -σσ- in Greek for the name Sāsān: rather, it seems it was usually spelled with -σ-. A recent WordReference thread about the ultimate etymology of the name (it seems to be unclear) linked to the chapter "Dynastic connections in the Arsacid Empire and the origins of the House of Sāsān", by Marek Olbrycht (2016), which says
The main component of the name Farn-Sāsān is the word ssn/Sāsān, which was in widespread use in Ancient Parthia, including the Nisa texts. The etymology of Sāsān is controversial. D. N. McKenzie and V. A. Livshits derive it from Old Iranian *Sāsāna, "Defeating Enemy". [...]
Recently, M. Schwartz has proposed another etymology of Sāsān. He sees a continuum from the ancient Syrophoenician form *Sasm to the Late Antique Greek and Aramaic form Sæsæn/Sesen. But his alleged Parthan Sesen for ssn is not convincing, for linguistically no links are discernible between *Sasm or Sæsæn/Sesen and Parthian ssm. Moreover, the occurrence of the non-Persian name ssn spelled in Greek Σασαν or Σασάνης in the ŠKZ inscription clearly implies that this is actually the Parthian name Sāsān.
A later section in this chapter titled "Sāsān in Roman and Armenian sources" seems to quote ancient texts in Classical languages about Sāsān, but I haven't found information about the original spellings used. The texts mentioned are "Agathias II, 27, 1-5: 1" and "Synkellos [p. 440.11-441.2 (p. 677.11-678.7 €SHB)]".
I would appreciate it if anyone could tell me more about the way this name was spelled in Greek and Latin of various eras.