I just did a 4400 mile road trip from San Diego to Chicago (along route 66) and back (along I-80) and MAN the stupid speed limit detector really wasn't working worth a crap.
To be fair, most of the time it saw speed limit signs correctly, including unexpected road construction limits. However quite often in Arizona, New Mexico and Texas, I would be driving along and pass a "65" speed limit sign, yet the car would act like it didn't see it and limit me to 55. Usually it shows the sign on the display, but for these it was like they weren't even there.
Similarly, in states I saw there are several signs and it just seem to confuse the car to no end. "Speed limit 70," "minimum speed 45," "truck speed limit 55." I forget exactly where I was but these three signs posted one after the other caused my car to think the speed limit was 70, then 10 yards later it was 45, then 10 yards later it was 55. I watched the screen in horror. lol.
So yeah, learned my lesson to be mindful of the speed limit detector: it doesn't always work, and our roadways can really be confusing!