SKU and variant key
In Engage the SKU (stock-keeping unit) is a standard article property. Elevate, however, refers to articles as products, and the variations of products as variants. Each product and variant has a unique key in Elevate, and to future-proof the Engage-Elevate implementation an Elevate variant should have a variantKey value corresponding to the article SKU in Engage.
At the moment there is no hard dependency on SKU/variant keys for Evolve features, but for the sake of future-proofing an implementation, we strongly advise you to make sure they align.