Google maps also isn't always accurate. There's no source of maps that's guaranteed to be 100% accurate all the time.

> 100% ... all the time

Because nothing meets that standard, it's not an applicable measure of quality. Also, it tends to lead to binary thinking: 100% or null.

But we live in a world of less than 100%, and there is a lot of variation: Five nines, 80%, datasets with just a few valuable records, etc. That's where the real-life questions are.

It is an interesting question. I've worked with a fair bit of geo-data, and found pretty much any sufficiently large geo-dataset, regardless of whether it's crowd-sourced or purchased from a commercial provider tends to have a fair number data accuracy issues.

If you spend any time on either OpenStreetMap or Google Maps in the rural US, and you are very likely to find both missing streets, and streets that have been completely hallucinated out of nothing -- mostly because they were both originally sourced from the US CENSUS TIGER data -- a US govt data set that tends to be full of errors.

OpenStreetMap contributors of often improve these issues over time (though it largely depends on if the area you care about has some sufficiently dedicated mapper).