In France, in Grenoble’s suburb, I used my Garmin Etrex 30 (GPS+Glonass) with my bicycle to record tracks.

I drove precisely at the junction between light and dark areas: https://www.mapillary.com/map/im/xFBBFuiCsI6Pu-WK4dsGbw

Now, you can see the report in JOSM:

Background are orthophoto and cadastre both in RGF93 (i.e. local datum that was mostly aligned with WGS84 in 1993).

So, even with a consumer product, we can touch the problem.