As a non-native speaker but a teacher of the English language I've come across the following question reading a pupil's report: Should she use the simple past or past perfect in her sentence?
Last week we came back from a class trip to New York. We planned (OR) had planned that trip half a year ago.
(meaning: half a year before NOW)
Although we teach that ago is a signal word for simple past, I would go for past perfect here, since the action of the second sentence clearly takes place before the first one and before the rest of what the report is about (the class trip itself).
How would a native speaker put it?