Hi,

The best practice for importing opening inventory in Odoo when using FIFO is to create backdated purchase receipts for each historical purchase. This involves creating purchase orders for the actual historical purchases and receiving the products with the receipt date set to the original purchase date. This ensures that Odoo generates stock moves and valuation layers with the correct historical dates, so FIFO will consume the oldest layers first when selling products. Using standard inventory adjustments is not suitable because they always create valuation layers with the adjustment date, which breaks historical FIFO. While direct manipulation of stock valuation layers is technically possible, it is risky and should only be done in pre-live setups by experienced users. For large volumes of historical stock, writing a migration script to automate backdated purchase receipts can save time and maintain accurate stock valuation and accounting integrity.

Hope it helps.