I think the amount of time gap between the two actions will dispose us to the use of the tense whatever best fits there . If the gap in the time is considerably of long duration , we tend to use past perfect tense and if the two actions are simultaneous or near simultaneous , we would find it too formal to use the perfect tense and thus we would go in for the progressive tense .

I have the knowledge of the use of this kind in certain announcements that read 'admissions going ' , ' repair works going ' and the like . At first they ,with their apparent lacking of the helping verbs ,hit me right in the eye but having come across the sentences of such kind particularly in advertisements or announcements , I have got used to them .