Contextual filter for an indirect taxonomy term? I know how to display similarly tagged items of a different content type in a view block (here is a good explanation and settings picture).

I have a scenario where the term IDs aren't directly associated with both content types. The term reference field on the page content type is attached, not to the view content type itself, but to another taxonomy that is attached to the view content type (the view content type uses a taxonomy that has a field which is also used in the page content type).

How can I filter my view to items that are "mapped to" the term?
To rephrase (to see if I understood correctly):
You have a content type pointing to term reference #1, that is pointing to term reference #2. You want to show the content that points to term #1, with the context being term #2.

In that case, you'd need to create a relationship (see Using Views Contextual Filter and Relationship to display reference on referenced node)

(The following explanation would work best with entity reference instead of term reference - I don't use that field type so I'm not sure the relationship exists with it)

But in short, you'd create a relationship to "referencing entity from field_term_reference" (the field on term #1 pointing to term #2). From there you could create the "referencing entity" relationship from the field on the content type pointing to term #1. The contextual filter would be to the term ID #2 using that relationship.