The site-wide rules for inventory.
Changing the costing method leaves the past alone
The costing method decides the order in which cost layers are consumed on the way out: oldest first (FIFO) or newest first (LIFO).
Changing it affects only later outbound movements. Movements already recorded, and the cost worked out for them, are untouched — the ledger is never rewritten.
So for a while after a change the inventory's value is the result of both methods. That is expected.
Identifier patterns apply only to new records
The SKU pattern and the PO number pattern are used for future items and orders. Identifiers already issued do not change.
The low-stock threshold here is only a default
"Low stock threshold" is the reorder point stamped onto newly created items. It does not change existing items, and each item can carry its own figure.
Zero means no default is applied.
Low-stock alerts have several destinations
An alert can go out as an in-app notification, as email to a list of addresses, or as a webhook call — each independent of the others.
These alerts order nothing; they only tell you. Ordering is the Reorder page's job.
The default warehouse
The default warehouse only decides which one forms start on. It moves no stock and does not prevent working with the others.