If a DVC member wants to check for you, they can tell you the current availability. We've worked with David's Vacation Rentals in the past (and have had some communications with the DVC Rental Store as well), and both were pretty up-front with us about the likelihood of getting the rentals we wanted for the dates we were seeking, both in terms of availability of rooms in our desired category/resort, and in terms of whether they would have members who'd listed points that matched up. If you're considering going through them, I'd contact them directly about it.
I'd hazard a guess that the Poly is easier to get than most, since its inventory is comparatively high (and so is the pricing in terms of points), but again, that's just a guess. We rented DVC points from David's for a 2-night Poly stay for our upcoming visit in May, but we made our request at 11 months, and it was able to be met within a couple of days. I had my heart set on it (bucket list item), so it was worth the extra cost to ensure we got it. Otherwise, we'd have waited until 7 months out.