Group stitching up conductors (8)

I believe the answer is:

maestros

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'conductors' is the definition.
(I've seen this in another clue)

'group stitching up' is the wordplay.
'group' becomes 'sort'.
'stitching' becomes 'seam' (I can't justify this - if you can you should believe this answer much more).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'sort'+'seam'='sortseam'
'sortseam' in reverse letter order is 'MAESTROS'.

Can you help me to learn more?

(Other definitions for maestros that I've seen before include "Distinguished music conductors or performers" , "Italian masters" , "Artists of consummate skill" , "orchestral conductors" .)

I've seen this clue in The Everyman puzzle in The Observer.

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