thanks for the response everyone. Just got another of the same messages, the count keeps going up.
I won't worry about it right now, google will likely find many more. Im confident they're handled correctly at this point. although I do suppose the more correct response code would be 410, I think we'll leave it at 404 for now as I am adverse to change after change after change.
On a note, our crawl rate had an increase of about 4x the usual daily rate. not sure if it's in direct correlation with this, but I'm assuming so for now, unless I see a lot of reports on others experiencing a crawl increase due to an upcoming update.