Loading document always second-class in determination (7)

I believe the answer is:

waybill

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'loading document' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe there's an association between them I don't understand?

'always second-class in determination' is the wordplay.
'always' becomes 'ay' (archaic term for 'always').
'second class' becomes 'b'.
'in' is an insertion indicator.
'determination' becomes 'will' (will can mean determination or desire).
'ay'+'b'='ayb'
'ayb' placed within 'will' is 'WAYBILL'.

Can you help me to learn more?

(Another definition for waybill that I've seen is " Goods list".)

I've seen this clue in the Sydney Morning Herald.

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