Instead of using low correlation methods of trying to extrapolate oversales from available seat maps, why not call United and ask the question?

There are HUNDREDS of threads with this exact question, and people always give these seat counter sites, then find out that they are rarely true indicators of what you want.

From UA.com, under "United Committment",
"We will advise inquiring customers if the flight on which they are ticketed is overbooked. United employees who have access to the information as part of their work will provide it upon customer request. We also will establish and disclose to customers our policies and procedures related to denied boarding, including any applicable requirements—such as check-in deadlines."

That seems to me to be much more reliable than trying to use information about what seats, that the web site has access to (not all seats are loaded into their inventory), to try to determine the answer to a question that UA says they will answer directly when prompted to.