Can’t check Apple warranty information on Apple’s checkcoverage site

I’m intending to get an iPhone 13 from one of individual resellers who have upgraded. Some have posted their serial numbers online for verification, but when I key in to search for warranty coverage, Apple’s official site only shows “valid purchase date” and “technical support eligibility” but not one more field stating whether limited warranty is valid or expired. How may I check the last bit? Appreciate some help.