And how can players distinguish that?
Perhaps. As noted, you are insulated from a lot of things because your group has remained functionally unchanged for decades. Even on this site, which leans older, "traditional", and GM-centric, your experience is quite far from typical. Plenty of players will now have personal experience with GMs that would pull shenanigans like this. That might not affect YOU. But it does affect plenty of people who might want to heed your advice.
No. What I'm saying is, you have not really done anything particularly meaningful or noteworthy by only revealing secrets that are now, functionally, irrelevant. Like finding out after you quit a previous job because you got a better offer, that there were free snacks in the break room that you never knew about, or that all those weird tasks that came down from on high were actually part of a hush-hush government contract all along, and thus there were specific rules for why certain tasks were assigned, or that all the times you got a promotion and someone else didn't (or vice-versa) there were actually well-defined and specific procedures which were sensible, just complicated. Like...you no longer care. It no longer matters why those things were ABC and not XYZ, because...it literally doesn't affect you anymore. Knowing how to advance in a workplace you don't work at (and almost certainly won't work at again) is useless information. It's nice to know that they weren't yanking your chain, but other than letting you know that they weren't doing that, there's nothing really gained from this information.
Again, I'm not saying it's bad, and I definitely didn't say that EVERYTHING FOREVER should be revealed. (It's worth noting, this is an example of inserting an extreme view I never said nor even implied. Folks on the "traditional GM" side of this discussion have been quite prone to call out ascribing extreme views to them. If that's a problem, I'd appreciate that that expectation apply to all.)
What I am saying, is that there's a lot more meaning to communicating the rules, or at least some of the rules, when that information still has a meaningful (NOT guaranteed, just meaningful) chance of mattering. That's a gesture with weight to it, because the rules are public knowledge. A failure to abide by them is visible. As I said (repeatedly), that kind of reveal means you as GM have skin in the game. There's no cost to you, no risk, no weight when you as GM already know that it almost certainly won't ever matter. There is some cost, some risk, some weight if you have good reason to believe it will matter again, even if not right away.
Hence why I said it wasn't bad, but it wasn't particularly good either. It's null information, because the impact of the reveal is largely null.
Separately from the above: Why does there need to be mystery in it? You say this as though it's axiomatic that every rule should be mysterious until it doesn't matter anymore. This is far from established (to say nothing at all about whether it is even true).