I read web fiction a lot and sometimes I notice sentences that, while being written in past perfect tense, might have been written in past simple tense as well.
He’d broken his glasses once, years ago. He’d done it in a childish tantrum, and it had taken days before he could get new ones. Back in the ugly days.
That hadn’t been the day the tantrums stopped, but it had been a lesson that had stayed with him. Rare, when he had so many terrible teachers.
What's interesting, the last sentence is past simple while everything else is past perfect, despite they seem to be talking about the same period of time.
My understanding of past perfect is that, when we talk about some event that took place at some time in the past (oftentimes expressed via past simple) and then we want to talk about yet another event that happened prior to the first (most recent) one, we use past perfect, like:
I couldn't open the door [the most recent event] since I'd left my keys [the most distant event] at my friend's place.
So, past perfect implies the existence of the most recent point, explicitly expressed or implied by context, but it doesn't seem like this type of timestamp was given to begin with. The sample talks about a chain of events happened some time back in the past, there's simply no "the most recent event".
It's not the first time I encounter this usage of past perfect in fiction. Is this kind of usage common and what does it mean?
I can't help but wonder: what is the subtle difference between them?