Salve:
I am having trouble translating this sentence in “The Arrest and Trial of the Conspirators.”
Res praetoribus nota erat solis,…
I can’t tell whether nota is imperative or perfect passive. If perfect passive, wouldn’t it be notata erat?
The thing had been marked by the magistrates alone. (Why no ‘ab’ before praetoribus?)
Gratias et Vale
salue elduce
You’re right about notata - the solution is that nota is a noun.
Therefore erat simply means ‘was’.
And a final aid: you’re right that ab is usually the preposition with which to introduce the agent. Could praetoribus solis be another case here?
Hope this helps: puto te posse 
I disagree, I would say that nota here is from the perfect passive of nosco, noscere, noui, notum. notare is the iterative of that verb and coincidentally has some similar forms, but they make little sense here. the correct translation then is “the matter is known to the praetors alone”. the dative of reference can sometimes be used where you would expect an ablative of agent, and with noscere is often so used in the passive (oops, I think I just answered amans’ test question, sorry!).
I considered nota as a form of nosco, too, and I acknowledge this possibility. But wouldn’t you translate res nota erat as a pluperfect, then? “The matter had been known to the senators alone”.
Having no context to go on, my idea was something like: “the thing was a sign to the senators alone”.
notae, -ae works, but res and nota in agreement seem to me the more obvious choice - the vocabulary of the book may decide which is the intended answer. I did translate that tense too hastily, but I would still use a simple past “was known” rather than pluperfect “had become known”.
Gratias Benissimo ac Amanti ago.
I get annoyed when W doesn’t entirely explain things, such as assuming the student should imply certain things. Example: the verb cognoscere means to be aware of, learned in something and the perfect means to know but I never understood what noscere meant and W doesn’t say.
Pax