Number on display indicates that they left seat empty (6)

I believe the answer is:

noshow

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'that they left seat empty' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'number on display' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'display' becomes 'show' (synonyms).
'no'+'show'='NOSHOW'

'indicates' acts as a link.

Can you help me to learn more?

(Another definition for noshow that I've seen is " One fails to attend".)

I've seen this clue in The Irish Times.

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