I had the same question, I'm not versed on manufacturing processes but "Just in time" would seem to imply inventory is nearly 0 and as parts come in, they are used for assembly and go right back out the door.
Perhaps they realized the limits of JIT and have looked at storying inventory based on the impact to assembly continuity?
> storying inventory based on the impact to assembly continuity?
It's always been about that.
JIT can be looked at as, "right part in the right quantity at the right time." That can mean "milk runs" where assemblies are delivered to the final assembly plant twice a day. An AM delivery where the last assembly is bolted to a car as the PM delivery arrives. Or it means "kanban orders" where 1 week supply of parts is delivered on a Monday and a refresh the next Monday. Or it means you buy in bulk and get 3 months supply at once.
JIT and everything around "Lean manufacturing" and the "Toyota Production System (TPS)" are ideals to strive for. Not everything in Toyota operates according to the ideals. There are certain fundamental things (e.g., stability in material, personnel, machinery, and methods) that need to be in place before starting to reduce inventory.
When suppliers have trouble with providing defect free parts, the orders start to increase in quantity and decrease in frequency. These can be subject to 100% incoming inspection if the supplier's quality comes into question enough.
Perhaps they realized the limits of JIT and have looked at storying inventory based on the impact to assembly continuity?