The most common and most likely answer to this crossword clue is the 6 letter word COUNTS
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More clues leading to the result COUNTS
Buddy explains!

The straight part
We know that "Adds up the number of/noblemen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case adds up the number of/noblemen = counts.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COUNTS mean?
COUNTS noun- The act of counting or tallying a quantity.
- The result of a tally that reveals the number of items in a set; a quantity counted.
- A countdown.
- A charge of misconduct brought in a legal proceeding.
- The number of balls and strikes, respectively, on a batter's in-progress plate appearance.
- An object of interest or account; value; estimation.
- To recite numbers in sequence.
- To determine the number (of objects in a group).
- To be of significance; to matter.
- To be an example of something: often followed by as and an indefinite noun.
- To consider something an example of something.
- To take account or note (of).
- To plead orally; to argue a matter in court; to recite a count.
- The male ruler of a county.
- A nobleman holding a rank intermediate between dukes and barons.
- Any of various nymphalid butterflies of the genus Tanaecia. Other butterflies in this genus are called earls and viscounts.
- (of a statistic) To be enumerated rather than represented as a proportion or percentage.