purchasing from non apple stores

Whoever you spoke to at the Apple Store was wrong.

The official purchase date, for warranty and AppleCare+ purposes, is based on your purchase date from the Authorized Apple Reseller, not when the reseller originally acquired the device from Apple. That means your Apple Limited Warranty and the eligibility window for purchasing AppleCare+ both start counting from the day you buy the device.

That said, sometimes the device might initially show an incorrect coverage date in Apple’s system — usually if it sat on the shelf for a while. In those cases, Apple lets you submit proof of purchase (like a dated receipt) to correct the coverage start date. This is especially common with third-party retailers or if the device was shipped but not activated right away.

So as long as you have your sales receipt from the reseller, you're good. You’ll have up to 60 days (sometimes extended to 1 year in some countries) to add AppleCare+, depending on your region and the product. You can check or add coverage at Check Your Service and Support Coverage - Apple Support or directly on the device in Settings > General > About shortly after activating it.

Alternately, you should be able to purchase the AppleCare+ plan from the Best Buy store you purchased them from.