Am 07.03.2018 um 21:01 schrieb email@example.com [SwissRail]:
I did the 3-Paesse fahrt, which at the time went from Interlaken OstPlease allow the world to change a bit within 30 years ;-)
This offer ended in 1987 and at the end it was limited to Tuesdays and Thursdays from 30 June - 1 Oct 1987. The timetable said that the intermediate stops could be different, depending on the weather conditions. An earlier timetable also said that it could be the other way round (Grimsel first).
From other timetables I see that it had the same timings as the daily service out of Meiringen. Seat reservation was mandatory. So they could decide, if the Interlaken bus also took the Meiringen passengers or if it ran independently.