Early warnings are between the Project Manager and Contractor, not the Client, Supervisor or, for that matter, Subcontractors, so the whether the Contractor 'told' the Client is contractually irrelevant.
In the absence of an early warning, the question becomes what would the savings have been if the Contractor had given an early warning ? If the PM can reasonably state that he or she would have instructed the Contractor to do something different than the Contractor actually did & hence save the Client money &/or time, then the PM should state this when instructing a quotation - see clause 61.5 - and the event is assessed as if the Contractor had given early warning and these actions were implemented - see clause 63.7. i.e. the Contractor gets less.
Otherwise, it makes no difference.