Hi BounceOnline ,
Apologies for any inconvenience caused.
Please note that we don't support WPALLIMPORT and I'm pretty sure it can't update inventory data for secondary inventories.
That said, the field should be updated because we don't change anything if multi-price isn't active for the product. If the product's multi-price option is active, the imported data should appear in the Main Inventory because we use the WooCommerce product metadata fields to store the Main Inventory info.
Best Regards,
José Andrés