I have been travelling the Montreux - Zweisimmen (the MOB railway - try not to labour too much on the 'GoldenPass' branding) on and off for 59 years (and I'm 59…)
Here's my personal 'FAQ':
The Golden Pass rail route:
Current tourist branding can be confusing
1) The true Goldenpass is just the MOB railway Zweisimmen - Montreux.\
If you are based in Montreux, you will be concentrating on the 'true' Golden Pass as far as Interlaken.
2) The Luzern - Interlaken railway is actually the Brünig Pass line operated by Zentralbahn (ZB), which dubs the regular trains "Luzern - Interlaken Express'.
It's OK but not spectacular scenery
3) The 'bit in the middle' (Zweisimmen - Spiez - Interlaken) is two branch lines of the full size main line BLS railway, with a mix of local trains (change at Spiez) and some through services Zweisimmen - Interlaken
** A few facts about the Montreux - Zweisimmen railway - ie the MOB (Montreux-Oberland - Bernois):
The Golden Pass is historically only Montreux - Zweisimmen, only more recent marketing branding takes the 'Goldenpass route' east of Zweisimmen to Interlaken and beyond to Luzern.
The Golden Pass is the touristic branding for the Montreux - Oberland Bernois (MOB) railway but after a few years of favouring 'Goldenpass services', the company decided it was losing its tradition and has reverted to putting the Chemin de Fer Montreux - Oberland Bernois name on publicity and train coaches.
*MOB pioneered the Panoramic coach concept on Swiss trains, starting in 1976.
There are now several versions of panoramic coaches in service, but MOB keeps changing its mind how to dub each service.
It hardly matters anyway as most modern Swiss trains have large windows, even if not officially panoramic. The key element of a ‘panoramic’ coach is ‘toplight’ windows above your head but in practice very few of the major views from panoramic trains are directly above your head, so the view through the normal side part of windows is normally fine.
You will get roughly the same scenic experience form any train on the MOB and reservation is not obligatory
Here is the timetable PDF for the MOB:
www.fahrplanfelder.ch/ fileadmin/fap_pdf_fiel ds/2019/120.pdf
It is very scenic, but the MOB route is far from being the most spectacular (although any dubbing of this nature is going to subjective and personal) in Switzerland.
I recommend using regional trains on the MOB (the real name for the Montreux - Zweisimmen railway). Again, this gives you the flexibility to get on a train at whichever time suits you.