That's not what I was talking about, but that looks useful for other purposes, thank you.
I've now discovered that if you zoom in as far as possible, all of them have the bed icon, apart from B, which has a dot. Why only some of them show at a more normal zoom level is still a mystery. But then, Google maps as a whole are pretty much a mystery to me. I never did find an answer to my previous question about how to get a description to show - and it still doesn't.
Anyway, it looks as if there's nothing I can do here to get my client's "bed" icon to show at less than full zoom, so I'll stop worrying about it.