My new MacBook coverage issue (sorry, we are currently unable to validate your purchase date)

That's completely up to Apple; it's not anything you can solve on your own. Most likely whoever you bought your Mac from didn't get the sale entered correctly. Either that or it's a glitch in Apple's database. Either way, your original receipt issued by the Apple Store or authorized Apple reseller you bought your Mac from should provide proof if the sale date should you need warranty service. But you can contact the store or Apple Support and discuss it with them.

Regards.