Hi,

First, prepare and clean your data. Separate your records based on date. Products (items) that already existed before 1/1/2025 should be created in Odoo first as products, with correct names, Internal Reference, categories, and opening stock as of that date. These products are required before importing any sales data.

Next, import master data first, then transactions:

1. Products (Items) – Import all products that exist in your store, even if they were purchased before 1/1/2025, using Odoo’s CSV import.

2. Opening stock – Set initial inventory quantities as of 1/1/2025 using inventory adjustments.

3. Sales Orders and Invoices from 1/1/2025 onward – Import only the sales orders and invoices dated after 1/1/2025 using CSV import (for simple data) or Odoo API (for large or linked data).

Finally, validate everything by checking stock levels, invoice totals, and customer balances to ensure they match your old system. This approach keeps historical products available while ensuring financial and sales data in Odoo starts cleanly from the chosen date.

Hope it helps