My DH and I both know our IQ's. We also know the IQ's of both of our fathers and mothers, and a few other first degree relatives of those people. Everyone in that group is between 140-ish and 17o-something on the old SB-LM, with two NT exceptions. Within that framework, it is amply clear to us that our DD is at least EG, and almost certainly PG. "Very, very bright" is sort of an expectation in our families. Our yardstick is basically one that runs from "bright" through "PG." It's hard to keep that in mind, but on the other hand, it makes DD feel less freakish, I think, so that may be a good thing.
DH was tested in elementary school; I was too, at least the first time, though the SB-LM was used on me when I was about 11-13yo, I think. Happily, this also means that those values are directly comparable to the other individuals whose results are known to us.
DH is HG and I'm well into EG-- my father was PG (170+). Everyone who knew my father has spontaneously remarked on how similar DD is to him. I'm out there enough that I can see how she thinks, even if I can't always keep up with her. My DH can't always follow her 'jumps' the way that I can, which makes sense in light of the numbers involved. She is doing things at 14 that I couldn't do until I was 18-21 (and then some, actually-- since she was about 10, she has done some things that I simply CANNOT do). Interestingly, I'd have said that the Ruf levels were full of... well, something... until relatively recently with DD. I had my doubts about where she was (HG/EG/PG) until she was about twelve or so, and then she took off. Again.
Anyway. We've never seen the need to have the number for my DD. Like your DS, there was never any question of admission to program content that was appropriate for her, and she was very readily identified as "GT" through sheer (half-hearted) performance measures. Whatever has been (realistically) available, she's had access to, so no need in our minds. Even without the number, a 3y acceleration wasn't a problem-- and wouldn't have been at our local B&M schools, either, which is saying something, as we have a LOT of TigerParents here. So the sum of that is that yeah, she's almost certainly PG-- everyone else seems to think so, at any rate, so we're okay calling it that too.
Knowing wouldn't gain us anything, and truthfully we question how accurate it would be if she refused to fully cooperate (and she might).
It's been a decidedly mixed bag to have it, in the experience of the HG+ among us. It was used as a way to 'shame/guilt' many of us for underachievement-- hopefully that wouldn't happen now, but still, the possibility to internalize it exists, certainly.
Life is about a lot more than that value-- it can easily turn into a burden, a legacy, an excuse, a prison, or a curse, after all.
