Hi Andrew
Far be it from me being more knowledgable than you, but P means "Posting error". That means the check was printed, but when the manual check batch containing the printed check was posted, the check did not post most, likely because the invoice was already paid by another check in the same batch. The second most common reason is that the check was paying a cash invoice with a duplicate invoice number.
You can ignore P status checks, for the most part - they are not in vendor history, are not passed to the GL, and are not outstanding. Just make sure that if you actually mailed the printed check to either fix the error batch, or reenter the check.
Steve Schwartz