Later Lodge camp ovens had the logo on the bottom as well. I would surmise yours being sold on the cusp of the change meant sets comprised partially of older patterns would be sold, with no point seen in remelting inventory on hand just to update markings. Maybe the cover patterns were updated first, and no urgency was felt to update the bases. I have seen photos online of a set such as yours including the original carton, so it's probably not unusual. Griswold DOs are seen with slant logos on one piece and the large block on the other. I expect the manufacturers didn't think the consumer would notice, or care.