I was asking the port locals on a place that had a maximum of 16 million gold in the port. 3 days later it said the port maximum dropped by 3 million. Does that mean the gold available to find in the port went down?

that wud make sense if he moved it or wutever

This specifically means that the top treasure is not as large as it used to be. Specifically, one of the scenarios is possible:

Scenario a)Top treasurer retrieved a big chunk of his treasury.
Scenario b)Top treasurer had his gold stolen. For a probation period of 7 days, his treasure will not appear at all as existing in that port. Which means that you now read the second largest treasure in port.

As a hint, you should always use this once before attempting to find treasure (if you have been preparing this for long).

Finally, it is worth mentioning that exploration % have not yet started to deteriorate on purpose. We will be taking final decisions on this (how frequently they will deteriorate) in the near future.