Products, customers and suppliers are history-keeping dimensions. Each carries the attributes a professional would slice by — for products: code, name, type, category, the unit the product is stocked in, brand, costing method, reorder level; for customers: code, name, category, billing country and state, currency; for suppliers the same shape — and each carries them as they were on the date of the transaction being read.
The practical consequence deserves a plain example. You sell a product in the "Beverages" category all year, then reclassify it to "Pantry" in October. A calendar-year report by category shows the product's sales under Beverages through September and under Pantry from October — because that is what was true when the sales happened. Last year's report does not change under your feet when someone tidies the catalogue today. Reclassify freely; history stands.