i'll try to explain why this is the way that it is. it's a rare form, so, if the following explanation doesn't make sense, you may wish to memorize the problem in this thread instead (or forget all about it, depending on just how wide of a net you want to cast in your studying).
when we use the present perfect, we don't usually have a second event, because the second 'event' is the present. on the other hand, when the time described in a sentence is actually in the past (because of the way the sentence is narrated), then whatever would normally occur in the present perfect must be translated into the past perfect.
here are two examples to illustrate.
it is december 2007; the world record in the discus throw has stood since 1986.
it was july 1991; the world record in the long jump had stood since 1968. --> but it was broken later that year
hope that makes sense.
when we use the present perfect, we don't usually have a second event, because the second 'event' is the present. on the other hand, when the time described in a sentence is actually in the past (because of the way the sentence is narrated), then whatever would normally occur in the present perfect must be translated into the past perfect.
here are two examples to illustrate.
it is december 2007; the world record in the discus throw has stood since 1986.
it was july 1991; the world record in the long jump had stood since 1968. --> but it was broken later that year
hope that makes sense.
