Looking for Dat of Manufacture codes for furnaces and boilers

Does anyone have links to complete Date of Manufacture codes for furnaces and boilers?

There are several books out there to help on this. The Carrier Bluebook, the Preston Guide, just to name a few. Go online most of these cost $65-$95

When I locate any heating mechanical over twenty years old, I simply note…

*The heating system was paced through it’s normal sequence of operating modes, with no obvious defects noted at time of inspection. However, due to systems age, it is clearly beyond it’s life expectancy, and replacement should be considered. Until then, I recommend annual maintenance from a licensed contractor. *