I just stumbled upon an old meta question about the name of our chat room, and a comment gave me the impression that the classical spelling would be conloquium rather than colloquium. (Let me ignore capitalization and comparing U and V in this question.) In cases like this, are both NL and LL used in classical Latin, or is one preferred over the other?
How do we know? It seems likely to me that later copyists would have changed such spelling details, so classical choices would only be visible in inscriptions — but this is only my guess.
If you have evidence for other similar cases of assimilation and can argue that NL/LL should behave the same, that is perfectly acceptable. The main interest of this question is more focused, but more general arguments are welcome. Notice that this question is about spelling, not pronunciation.