Whilst things like site diary sheets and invoices are all important records for a Contractor - they have very little relevance when it comes to assessing compensation events. Clause 63.1 states that you use actual Defined Cost for work already done, forecast Defined Cost for works not yet done plus fee. The important switch point between actual and forecast is when the PM gave the instruction to change Works Information, or for all other events when the compensation event was notified. Therefore the majority of compensation events should be based upon a forecast of what would have been reasonable (including sensible allowance for risk). Just because you have done the work before the quote has been agreed does NOT mean that you revert to actual cost - hence I see no significance for diary sheets etc.
Hindsight should not come into the assessment! Even if you have diary sheets showing it took ten men ten days to do an activity - who's to say they did not go slow and drag it out? On the other side an Employer might say "why should I pay for risk that I can see did not happen?" Well, the answer is that for the same reason the Contractor can not claim for more risk than they allowed for in their quote if it was worse and it has not yet been agreed.
Hindsight should not come into the assessment! Even if you have diary sheets showing it took ten men ten days to do an activity - who's to say they did not go slow and drag it out? On the other side an Employer might say "why should I pay for risk that I can see did not happen?" Well, the answer is that for the same reason the Contractor can not claim for more risk than they allowed for in their quote if it was worse and it has not yet been agreed.