Here's why:
* No centralized database: There is no central record of every live television performance, especially those on public television.
* Decades of performances: The group performed for decades, and their appearances on public television likely spanned many years.
* Mary Travers' passing: Mary Travers passed away in 2009. Any public television performances after that would have been with only Peter Yarrow.
To find a specific date, you might try:
* Searching online archives: Some public television stations have online archives, though these are often incomplete.
* Consulting with music historians: Experts on Peter, Paul and Mary might have details about their live performances.
* Checking Peter Yarrow's website: His website might list his performances or have information about the last appearance with Mary Travers.
While it's difficult to pin down an exact date, it's likely that their final live performance on public television occurred sometime before Mary Travers' passing in 2009.