Premise:
"It is not always clear whether there were long-term positive outcomes from these trials since referral has been the outcome variable most often studied."
Hypothesis: You can not be sure whether anything positive came from the trials.

yes

Premise:
"I don't know, because I never saw her. "
Hypothesis: I did not see her, but I heard her voice.

it is not possible to tell

Premise:
"It was soon flourishing; with its natural harbor that attracted ships, Hong Kong leaped to the forefront as a base for trade."
Hypothesis: Hong Kong was soon a large port for trading.
yes