Investigation has shown that the Absolute Pointer Protocol (APP) isn't available during startup, even with the Dell BIOS upgraded to revision A10.

You can determine if the APP is available with the UEFI-based tablet test tool (for details, see KB78050 - How to use the Drive Encryption UEFI testing tool to verify if your tablet responds to the touch interface). During a normal boot sequence, during testing, the UEFI-based tablet test tool doesn't allow you to use the touch input. But, after starting your computer and enabling the One Time Boot menu option, the APP becomes available and the tablet test tool tests are successful.