Moderator note: Split from this thread. This is exactly what I have thought. However, the passive can also be a present perfect ("noun that/which has/have been done"), besides the present and past tense. But my guess is that "The car stolen was mine" can only correspond to the past passive "The car that was stolen was mine", because no adverbs and no more context is there; only the past auxiliary "was" (the italicized one before "mine") leads us to predict that the hidden tense of the participle "stolen" is also a past one. I am, however, not sure whether sentences like "The car stolen is mine" are technically correct and whether it can mean "The car that was stolen is mine" or "The car that is stolen is mine". I know the latter sentence (or interpretation) is a bit awkward without an adverb like "always". I don't know whether my guess goes together with native speakers', however.