The contracted customers might know to a certain extent in...

The contracted customers might know to a certain extent in contract manufacturing as some companies can be open book in terms of margin.

But what customers would not like is their competitors knowing how much they pay for contract manufacturing (which would be evident if HLF publishes margin in their announcement).

Really the term competitive advantage becomes meaningless if any sort of margin is published on a contract level.

Depends on industry though, for example, nbn provider companies can provide gross margin on a customer level because nbn costs tends to be known industry wide.