Earlier quoted context omitted.
Your third example isn't valid. It needs a bit of tweak. Tarou ga Noriko wo mita toshokan The particle "ga" and "wa" both introduce a topic. But in a phrase to explain a noun, we use "ga" exclusively. Your main point still holds, in a sense that "Tarou ga Noriko wo mita" is a valid sentence. But to be precise, "mita" in those two sentences are different conjugated forms; it just happens that two conjugated forms are…
> The particle "ga" and "wa" both introduce a topic Forgive me for saying this, since you seem to be a native speaker, but don't you mean that they both introduce the subject , not topic (using 'topic' as a linguistic term)? "Wa" would be the topicalising subject marker, denoting known information: Tanaka wa nihon ni itta. Tanaka went to Japan. -> As for Tanaka, he went to Japan. Tanaka = known information (i.e. Tana…
Your explanation of 'ga'/'wa' is spot on as far as I can understand as a layman of native speaker with standard Japanese grammar education in Japan but no advanced linguistic degree.
I'd say that, because 'wa' emphasizes the introduced subject as the center of interest, it isn't used in the subordinate clause.
Tanaka ga nihon ni itta hi. (The day Tanaka went to Japan) ; ok - the interest is on 'hi'
Tanaka wa nihon ni itta hi. ; invalid