Hi Tom Mcfarland,
If we are talking about historical folks, I'm always interested in learning if there is some historical justification for the information and findings about which we set out to collaborate. This isn't always apparent from the default Ancestry public tree citation.
First, most of the default citations to Ancestry's public trees are designed for use by their subscribers, rather than the wider community.
Not everyone is able to view the tree inforamtion. This means not everyone is able to know if there is some underlying source that supports one or another associated information bit.
Second, even those who are able to view the tree are only sometimes readily informed about whether the findings were based on work with historical records. Sometimes the associated source reported is another tree, on which, indeed, the information was devised from another tree ... and so on.
All sources are subject to error, so just because the citation wasn't so informative doesn't necessarily mean the information is amiss.
At least in my experience, when someone makes a change you don't understand, the best thing to do is to post a message or inquire directly of them. Share that you are not able to follow the change and would like more information, if it is available.
Sometimes the other collaborator doesn't have more information. Especially if the new information poses a conflict in the record, a G2G question, focused on the information and possibly seeking historical records, logic and reasoning in support of same, might be a good next step.
Hope this helps.