At what point on the project is agreement on schedule delay finalised?

You can use all the approved VO's to build your EOT claims inlcuding the trends. It should be a strong case as the VO's are not part of the original contract. Build a story using delay analysis based on the raised NOD's, TQ's, Queries, Daily Reports, VO's, SI's and any documentations that can proved that the project has been delayed. Weekly Time Impact Analysis (TIA) is a good approach to build the story and how the delay impact the project. Then create an overall as-built of the schedule for comparison.

if delay notices were put in and responded to by the Client and the delays and values settled and paid and were covered by VO's as the project proceeded I dont see where the owner has a case you cant back tarck on all of this agreed to and SETTLED delays.

Thats like buying a car or a house and going back and say hey I want to renegoiate the price again. 

You are just burning everyones money to crete this and then review this. So if you go through with this are they going to come back again and say oh wait I want to look at it this way. 

There are no mulligans or do overs. Let sleeping dogs lay 

Zoltan, but are things settled. Only the Final account settles things contractually. 

If a Client issues a number of VO's they must have an accumulated effect on resources and progress which you could not have anticipated when the first ones were priced.

Surely you can accept a VO with conditions?

Rodel, yes we did all that as we progressed the work. But is it legitimate to have a second go at the end of the project as a negotiating ploy with the global delay claim to settle the final account?

Yes, if the final settlement is not yet agreed, you can always build a case for negotations and backup the claim. Once agreed and signed, then that's final. It's very rare that another opportunity came to open the case.