The Level I or milestone summary schedule (MSS) is usually
a part of contract. MSS includes both intermediate & completion milestones along with access dates between various contractors. Detailed schedules generally
are not a part of contract as it’s a dynamic document. For ex., you may plan with
certain philosophy and when it comes to implementation you choose other, but whats important is you stick to agreed dates.
For EOT claims, importance of detailed schedules cant be ignored. Its important to analysis the critical path to identify the ownership of delays and for the same both the planned Level II/III and current schedule comes handy. For instance although dates as per contract schedule could not be met however there could be a critical task which was kept on hold for which contractor may not be responsible instead the other party was culprit. I think its not possible to define every level II/III critical interrelated-task in contract document and that’s where the schedules has a greater role & cant be ignored.
In the nutshell, when it comes to EOT claims leading to arbitration it all comes down to the way contract has been formed. Having said that, with right backup of historical data (schedules, meeting notes etc.), argument can be made to justify your case.
Hope this helps,