According to the link you posted, inventory has risen 3.6% in the past month, 11% in 3 months and 36% in the past 6 months. I think we will agree that this has a component of seasonal cycling, but it also shows that inventories are rising, not staying flat as you claim. I am not sure of the “normal” cycles, but the next couple of months will be interesting to see if inventory rises or falls. I think a fall would be normal while a rise would be abnormal.
Given the fall off in sales, the more important number is the increase in months of inventory.
