Final answer:
The fort in Nassau was observed to be in disrepair 18 years after its construction. The exact year is not provided, and without additional context, it cannot be determined.
Step-by-step explanation:
Based on the provided condition statistics, deterioration was observed 18 years after the completion of the fort in Nassau. Since the specific year of Nassau's disrepair and ruins of the fort was not provided, it is impossible to pinpoint the exact year without additional historical context. However, we can infer that the fort went into a noticeable state of disrepair 18 years following its original construction date. Additionally, the refectory was hit by one bomb, which may have contributed to the state of disrepair, though the exact impact of this singular event on the fort's overall deterioration is not specified.