The Custom Fact, Warranty Expiration Date, is a best guess on warranty information based on the device Serial number. In the Fall of 2020 Apple has started using random serial numbers on all new devices, therefore the best guess algorithm will not be as accurate as desired. Therefore, there is no programmatic way to know accurate warranty expiration dates on Apple devices.
Addigy is actively looking to build in more accurate warranty information that is programmatically accessible. For those who need warranty information that can be pulled programmatically, please create a Feedback with Apple and provide this information for MDM vendors to access. You can reference our Feedback: FB7682701 in your feedback with Apple.