An additional element to cover in your question is the fact they are waiting to see the full effect of a CE before issuing it. That is not contractually or practically what could be done. The Contractor should price what they know at that point including for reasonable risk, and again any variables could be dealt with by Project Manager assumptions so the quotation could be ring fenced at that point. If the assumptions turn out to be incorrect, then that would be revisited as a new compensation event.
For example, if the Contractor was unsure what the ground conditions would be at invert level for a new drainage run, the PM could say “assume good solid clay at invert level”. This means the Contractor does not have to price for worse ground and over dig which would take time/cost. If it turns out not to be good solid clay, then any extra over incurred due to worse ground would be a new CE - but only that element. The rest of the original CE stands.