The answer to your specific question is enough evidence to prove your entitlement to the Project Manager. This will be both in terms of the detail of the cost, but also impact upon the programme.
However – the better answer to your question would have been to prove this as you have gone during the seven month period. Typically on a project you are required to submit a revised programme every four weeks or every month. On that programme it is a requirement to show a planned Completion and Completion Date milestone. Any period that your planned was moving beyond the Completion Date then you should have notified a compensation event (not an early warning) at that time assuming it was one to justify that that event had caused the issue.
The idea with NEC is to justify time delay as you go not in a big chunk at the end. An early warning is notified when there is an issue that COULD affect in simple terms time, cost or quality. As soon as this IS an issue that IS affecting time, cost or quality then it should have been notified as a compensation event and a quotation submitted. If it is difficult to forecast at that point then Project Manager assumptions can be used to caviat what the quote should be based upon.
However – the better answer to your question would have been to prove this as you have gone during the seven month period. Typically on a project you are required to submit a revised programme every four weeks or every month. On that programme it is a requirement to show a planned Completion and Completion Date milestone. Any period that your planned was moving beyond the Completion Date then you should have notified a compensation event (not an early warning) at that time assuming it was one to justify that that event had caused the issue.
The idea with NEC is to justify time delay as you go not in a big chunk at the end. An early warning is notified when there is an issue that COULD affect in simple terms time, cost or quality. As soon as this IS an issue that IS affecting time, cost or quality then it should have been notified as a compensation event and a quotation submitted. If it is difficult to forecast at that point then Project Manager assumptions can be used to caviat what the quote should be based upon.