The Polaris part number is correct for the bag you actually get, which is the OEM single-zipper all purpose bag. In my opinion it's a better bag anyway. The double-zipper bag shown is supposed to have more capacity in reality it does not collect any more leaves than the actual bag you get. Plus, the double-zipper bag is harder to empty due to the way it's configured.
Ordering from Sunplay saves you $10 each off the best price you'll find anywhere and if you order three of them, you get free shipping, too.
As everyone knows, these bags don't last forever so having a spare around never hurts. I keep two bags in use at all times. When one gets full, I switch to the other and set the full one out to allow the debris collected to dry, which makes it much easier to empty.