The second year was the most prone to error, as this was an ancient ritual.
Ancient rituals were a major category of rituals. This type had no tier divisions, the choice of materials was extremely flexible, and there were no fixed templates. Everything had to be planned and calculated from scratch.
The advantage was that they weren't limited by Power Level or even class. Even a mortal could perform one, as long as they fully grasped the ritual's principles and had the necessary materials.
The downside, however, was the extreme difficulty. For the vast majority of ancient rituals, the idea that a mortal could perform one was purely theoretical.
Therefore, as long as no major problems arose after the first year of operation, a casual glance would suffice for the next nine. You wouldn't even have to come yourself; sending a Servant Demon would be enough.
Otherwise, it wouldn't be called a routine inspection.
