I’m thinking at the moment specifically about Calyptocarpus vialis because I made an entry for it and it was flagged as being introduced into Travis County by anthropogenic means. I always thought it was native, so I did some research and found this article, which seems to indicate it is native to Travis County.
Looking at the details for this species here, I see a list of places where it’s found and how it was introduced, but I don’t find a listing of where it’s considered to be native. I suspect that feature exists and I simply don’t know how to access it.
Amy user can add or update that information. It is possible to add a comment indicating what the source of the information is, but it is not mandatory, and honestly, most folks do not complete that section.
Low level such as county level information on plants etc often has contradictory information online.
On the status tab of the taxa page, you can see the first 100 places that have a status entered (unfortunately there is no paging function to see any beyond the 100). clicking the View link to the right will show the details, which includes the comment section where a source could be entered.