That particular tag is for the tankless that is installed inside the Boiler.
You’ve got yourself an original Boiler there. I see these oldies every week. If there’s no tag and no obvious defects, I simply annotate in the report…
*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. *