What is the difference between:
Most of the seated customers who were patiently waiting for this signal immediately grabbed their suitcases...
and
Most of the seated customers, who were patiently waiting for this signal, immediately grabbed their suitcases…
Thank you, and you make a good point, above, nickel.
For some reason I was thrown by the fact that we were talking about "most" (of the seated customers) and not "all" (and I was trying to get my head around that detail).
So it wasn't immediately clear to me whether the extra information (i.e., those who were patiently waiting for this signal) was essential or non-essential
I need to compare it to something like this to make sense of it (but I'm not sure if it's simplifying things - and it's a lame example, I know).
Most of my siblings, who are heavily tattooed and living at home, grabbed their suitcases. vs My only brother, who is heavily tattooed and living at home, grabbed his suitcase.
In the second instance, "who is heavily tattooed and living at home" is definitely non-essential (as we've already identified that it's my only brother).
In the first instance, it isn't immediately clear to me - but I can now see that it is non-essential (despite the fact that not all of my siblings who are tattooed and living at home grabbed their suitcases, it is still non-essential to "most of my siblings" or "most of the seated customers" who did - and we know, for certain, that those who did - grab their suitcase, that is - are all heavily tattooed and living at home).
So, analogously ...
Most of the seated customers, who were patiently waiting for this signal, immediately grabbed their suitcases (the commas do come into play).
Do you agree with my line of reasoning?
I've also taken your other advice on board; although, I'm still confused with "happened to have been".
https://www.google.com.au/#q=+"happened+to+have+been+"+
Expressions like ...I happened to have been in the room/train carriage when it happened (or when I first saw him), or James, who happened to have been in the room at the time, when I first saw him .... are quite common.