My experience has been that pretty much anything public land is pretty accurate since those surveys are done regularly and are digitalized. A lot of very rural areas where private property is adjacent to private property tends to be a little less accurate as a lot of those counties and townships are not keeping up with the surveys digitally. The map apps can only use the latest version of what has been digitalized which are often very outdated.
Edit: I'm looking at that and that is a piss poor explanation. No more posting from my phone. Let me try again.
I have a friend who got into cartography (that in no way qualifies him in the field of property lines its just a statement on how we came upon this knowledge). He often finds himself close to and sometimes crossing private property lines. I went with him to the county clerk office (small town) and we asked about how we can get access to current property lines based on recent surveys. They explained that it would be tough for the county we were in because they don't make the surveys available digitally unless a request to do so comes from the state. So depending on when the last request was and for what area it was requested, the survey data this is publicly available by the state (in digital form) can be up to 30 years old. I imagine older depending on what part of the country you are in. That being said, public land is surveyed regularly and made available immediately in digital format. Therefore it is often much more reliable. Areas where private property is adjacent to private property is where some of the inconsistencies seem to be the most prevalent.
As another note, you may be surprised by the amount of landowners who think they know where their property lines are but truly don't.
