Judge a very good Köchel number for composer (7)

I believe the answer is:

janacek

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'number for composer' is the definition.
'janacek' can be an answer for 'composer' (I've seen this before). I am not certain of the 'number for' bit.

'judge a very good kochel' is the wordplay.
'judge' becomes 'j' (abbreviation for judge).
'a' becomes 'an'.
'very good' becomes 'ace' (I've seen this before).
'kochel' becomes 'k'.
'j'+'an'+'ace'+'k'='JANACEK'

Can you help me to learn more?

(Other definitions for janacek that I've seen before include "Czech composer known mainly for operas" , "Czech composer (The Cunning Little Vixen)" .)

I've seen this clue in The Times.

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