(14) He died after he had been ill for a long time.
(15) She told me his name after he had left.
In a 1989 paper titled "Perfect and pluperfect: What is the relationship?", Raphael Salkie discussed the above pair in the following paragraph:
If the pluperfect in (14) is replaced by a past (...after he was ill for a long time), the result is bizarre, as Bouscaren et al. note (1982b: 77). (14) indicates that the illness was relevant to his death - it is natural to infer that it was in fact the cause of it. Using the past tense instead suggests that the speaker is not asserting any relevance relation between the two events, but in that case, why mention the illness at all, let alone in a subordinate clause straight after mentioning the death? In (15) the relevance relation indicated by using the pluperfect suggests that she deliberately waited until he was out of the room before revealing his name. Substituting the simple past (...after he left) does not, however, lead to strangeness in this instance; the subordinate clause in this case merely functions as a temporal anchor to let us know when the name disclosure took place, without the idea of deliberately waiting. As Bouscaren et al. point out (1982: 77), the relation between the two events is stronger in (14) than in (15). It would be odd to just use the illness as a temporal anchor given the close relation between the illness and dying; hence the oddness of (14) with the simple past.
Let me show the simple past version of (14) again:
(14') He died after he was ill for a long time.
According to the cited paragraph, particularly the boldfaced portion, Salkie seems to be saying that (14') is bizarre because we can't normally think of a context where the illness itself does not lead to his death. But I think I can think of such a context. For example, an old man could have died after suffering for a long time from a chronic but non-terminal disease that did not have any relevance in his death. In this context, the speaker might want to add the information about him being ill for a long time just to convey the idea that he wasn't free from disease before his death.
Does this mean that (14') might work in such a context?