LOL yes exactly this. I also work in GIS, and specifically in this particular field.
I'll add to everything you just said, plus anyone who has ever used Google Maps, should know that some of their stuff is out of date, some of it very out of date. Parcel data changes all the time. I am willing to bet that whatever Google maps uses is significantly out of date. The data also tends to be pretty expensive also to acquire as its maintenance is also. So anyone that uses this as anything other than to get a general idea is fooling themselves. The world of land registry and titles is improving, but much of it is stuck in an archaic system, Some of which is due to the simple vastness of the legacy records out there, and also due to some specific legal requirements that exist. I have access to systems and data that the public doesn't, and even then, to get a definitive answer, you need go through a more manual process.
As you say, EVEN going through the manual process can be a challenge (if doing it for legal purposes), and a bit of a historical lesson. Depending on when and where the land was surveyed different methods may have been used. I recall my Dad who was a lawyer looked into some land my grandfather owned, which ended up being some of the first land given out by the King. It pretty much pre-dated any kind of survey method, and was mostly based on features that may or may not exist anymore or that may have changed. All hand written, in an ancient book. I also recall an example when I took a course on land registry about a property dispute, where the description included a river, which of course changed its course to give more land to one land owner, and less to another, then trying to prove the old track of the river... etc... In some instances more art than science unfortunately.
Anyway it is still pretty cool that the software is free, and it does include some of this information. Though I do see it causing headaches when people in the public using it, assume it is accurate, take it as gospel, then make decisions or engage lawyers/land registry/government into it... Hopefully there is a big disclaimer on the data (not that anyone will read or pay any attention to metadata in my experience).