Yes, that is correct. Be happy you'll still have tires to buy
All BFG's sold after 2/15 (I think that was the date) are marked with a "D", and are for dirt use only, as the dirt drivers have no other option. I just hope they have enough tires for the dirt drivers to last until a new tire is picked.
I've heard, but not confirmed, that 600 is out of the BFG's, it's whatever the dealers have in stock only, then dirt guys are S.O.L.