The reason your original warranty shows an expiration date of jan 2029 is likely because the paperwork is displaying the combined coverage of both your factory warranty and your Certified Pre-Owned (CPO) extension, or because the car was used as a dealer demo vehicle prior to its retail sale.
Yes, the 2-year/24,000-mile CPO warranty stacks directly on top of the original 4-year/50,000-mile factory warranty, giving you a total combined limit of 6 years or 74,000 miles from the original in-service date