What does "duly" mean in the phrase "duly noted"?

Solution 1:

Duly is the adverbial form of the adjective due. It means either properly or punctually, and can be replaced by either word felicitously. So duly noted means correctly or appropriately recorded.

Duly noted encompasses only a tiny fraction of the usages of the word: this Ngram should be sufficient to illustrate:

Duly is as independent as it could wish.

Solution 2:

Contract terms and compensation are relative to this issues scope, size and workload. Increase to size and content shall be duly reflected in compensation.