I'll snap a photo of the txt on the head unit...and again, we should hopefully hear from someone out there w/ an expired data plan who can confirm what works for them...
I have an expired data plan for a 23 suburban. Connecting vehicle to my phone's hotspot enables built-in Google maps to work but the speed limit sign remained "--" for me in the few minutes I tested it this past weekend before I switched back to using Android Auto since it responds more quickly than the built-in system.
If the speed limit sign is reliant on downloaded maps, that may be why mine didn't register since it likely wasn't connected long enough to download any maps. I can do some more testing this weekend when I get the car back from the dealership where they're having to repaint the passenger door for a paint defect.
Agree with others that the mandatory subscription to make the car work is a load of crap. I'm interested to see if the just-announced release of Waze as a built-in Android Automotive app (first being rolled out outside the US) will enable offline map use without a data plan. One can hope but I wouldn't put money on it.