Not only that, but how would engineers, for example, know how much money was saved or earned from blah feature or project unless that was explicitly shared with them? Time saved or usage can usually be measured by the engineer, but money is a lot trickier.
Like I'm able to say a speech application I made was used in over a million calls, because I looked at the database and saw that many call records in there. And I'm able to say that I set up an one-click 30 minute devops process for deployment that was previously done over the span of 4-8 hours manually with multiple engineers onhand in case things went wrong (and they often did due to user error), because I was physically present during those manual processes and could directly compare and contrast the time difference.
But I can't say it "saved the company X million dollars" or whatever because I wasn't in management and didn't have those figures shared with me.
At least not honestly. I could make some bullshit up (I don't, but I could), like you said, and how are you going to verify it? Do you think a past employer will confirm or deny those figures if you call? You'd be lucky to get much more than confirmation that I worked for them and what dates at this point, thanks to all the liability around it. Also there's no guarantee that they know (or remember offhand) themselves, maybe they weren't on that project.