if call #1 is the file, call #2 is the file + the question, call #3 is the file + a different question, then yes.
and consider that "the file" can equally be a lengthy chat history, especially after the cache TTL has elapsed.
As far as I can tell it will indeed reuse the cache up to the point, so this works:
Prompt A + B + C - uncached
Prompt A + B + D - uses cache for A + B
Prompt A + E - uses cache for A
if call #1 is the file, call #2 is the file + the question, call #3 is the file + a different question, then yes.
and consider that "the file" can equally be a lengthy chat history, especially after the cache TTL has elapsed.