I'm not sure why you feel the above are examples of outright lies.
A few years back, probably 2018, we met up with friends in the park. They asked if they could join us for dinner. I asked the hotel concierge for help in modifying the ADR. In short, this is exactly what the concierge TOLD us (to do).
What happened to us happens to other people at WDW every day. So YES, you can add people to your ADR, and the way to do it is to list your party size when you arrive at the podium. I imagine there are some exceptions, but the podium hosts field questions like this all day. It isn't rude to ask, nor do the hosts get upset over it.
A VERY good reason to NOT do this though is that we were seated very late. Instead of 7:15pm, we were seated more like 8:30pm. That's the trade-off. By the time we were seated, it was well past the time most people eat dinner.
It is a similar situation at the hotel guard posts. Most of the time they will happily wave you through. Generally speaking, if you want to dine at a value, mod hotel or most DVC's, you can. You do not need an ADR. The deluxe hotels are the places that will sometimes turn you away. Disney doesn't want people to park at the monorail resorts to visit MK, nor do they want people to park at Bwk/BC/YC while they visit Epcot/HS. That's all. I just did this at the Boardwalk a few months ago. We asked if we could park to pick up food from the new deli, and the guard said we were fine. In short, he did not care.
The purpose of these forums is not to police each other over the way we think WDW should be run, IMO. Our purpose is to provide each other with helpful information. At least, that is what I try to do. Disney is complicated, and even after many visits, I often have questions like two examples above.