As far as I can tell, you are looking at pairs of sentences where present and past might seem to be interchangeable.
A scenario: Yesterday, your colleague told you a story about a person called Weininger. Today, your colleague starts talking about Weininger again. If you don't remember yesterday's interaction at all, you would say Wer ist das denn? However, if you remember the name but not the story, you would say Wer war das nochmal? In this case, the particle nochmal makes the intended meaning clear enough that Wer ist das nochmal? is equally possible. This is what happens in your examples one and six: they're about the distinction between learning something for the first time (present) and having learned something before, but not being able to recall (past).
Second scenario: Your colleague has bought a new watch. You could ask either Was kostet die Uhr? or Was hat die Uhr gekostet? The two can be very close in meaning, the potential difference being that the present refers to a regular market price and the past to some special deal: Normalerweise kostet das Ding über tausend Euro, aber mich hat sie nur fünfhundert gekostet. (There are other possibilities, of course. Was kostet die Wohnung? might refer to monthly rent payments, Was hat die Wohnung gekostet? to a purchase.)
This might be what is happening in your example Wie viel hat deine Jacke gekostet? Usually, kosten is a static and durative event, but here it is a bounded event, referring to the purchase of a particular jacket that took place at a specified time. This isn't due to the past, but rather to the ambiguity of the jacket either referring to a model or an instance of that model.
Dieser Chip (model) hat vor einem Jahr noch über tausend Euro gekostet. (static, durative)
Dieser Chip (instance) hat mich damals über tausend Euro gekostet. (bounded)